From May to August 2014, in designated isolation areas, the forces of the anti-terrorist operation (hereinafter - ATO) managed to:
- liberate part of the territory of Donetsk and Luhansk regions that was under the control of illegal armed formations of the Russian Federation (hereinafter - IAF RF);
- restore and reinstate state authority in the cities of Mariupol, Sloviansk, Artemivsk, and other settlements;
- encircle the group of IAF RF in the area of Donetsk and Horlivka and create certain conditions to stop the supply of weapons and ammunition to them from the Russian Federation, and as of 30.07.2014, take control of over 250 km of the state border in Donetsk and Luhansk regions.

However, as of 07-11.08.2014, the situation in the area of the ATO in the territories of Donetsk and Luhansk regions, including Sector "B", remained complicated.

The main efforts of the illegal armed formations were focused on restraining the actions of ATO forces. For this purpose, the accumulation of forces and means of IAF RF continued in the areas of the settlements of Shakhtarsk, Torez, and Snizhne. The most complicated situation was in the cities: Donetsk, Horlivka, Luhansk, Sverdlovsk, Pervomaisk, Ilovaisk, Snizhne, and Stakhanov.

In the settlements, there was a significant concentration of forces and means of IAF RF, namely: Horlivka - up to 800 people (with further increase to 3,000), Yenakiieve - up to 2,100 people, Ilovaisk - a grouping of militants consisting of 2 battalions of 7 companies each (approximately over 1,200 people).

At the same time, from 07-11.08.2014, the grouping of the Armed Forces and Internal Troops of the Ministry of Internal Affairs of the Russian Federation along the state border of Ukraine numbered up to 32 battalion tactical groups (hereinafter - BTG) and 3 company tactical groups (hereinafter - CTG). In total, the number of personnel was no less than 45,000, tanks - up to 160 units, infantry fighting vehicles (hereinafter - IFV) and armored personnel carriers (hereinafter - APC) - up to 1,360 units, artillery - up to 350 units, multiple launch rocket systems (hereinafter - MLRS) - up to 130 units, combat aircraft - 192 units, helicopters - 137 units.
The command of the RF Armed Forces continued active measures to increase the grouping of troops near the state border of Ukraine by deploying military units and formations reinforced with artillery. The combat training of the RF Armed Forces continued near the state border of Ukraine.

The main efforts of IAF RF were aimed at restraining the actions of ATO forces and maintaining control over the settlements of Yasynuvata and Khartsyzk to prevent the complete encirclement of the city of Donetsk.
In the cities, measures were taken for the engineering equipment of positions, and the mining of access roads and transport infrastructure facilities was carried out.

In accordance with the decision of the ATO Headquarters, as of 07-08.08.2014, units of the 40th battalion of territorial defense of the 17th separate mechanized brigade, as well as parts of the forces of 3 BTG of the 51st separate mechanized brigade, blocked the city of Ilovaisk, thereby ensuring control over the main transport communications.

During the period from 12-23.08.2014, based on the decision of the ATO Headquarters on the territory of Donetsk and Luhansk regions from 11.08.2014, an operation was planned to defeat the main forces of illegal armed formations that were part of the terrorist organizations "DPR" and "LPR" in the cities of Yenakiieve, Horlivka, Pervomaisk, Stakhanov, and in the adjacent areas; complete blockade of the cities of Luhansk, Donetsk, and Makiivka; narrowing the outer circle of isolation and restoring the activities of state authorities and local self-government in the liberated areas.
It was also planned to complete the clearance of the city of Ilovaisk in Donetsk region from terrorists and take it under control.

This would allow for the complete blockade of illegal armed units of the mentioned terrorist organizations in the city of Donetsk from the south and would facilitate the advance of ATO forces towards the city of Zughres, as well as other forces and means towards Khartsyzk - Zughres from the north, for the complete blockade and liberation of the settlement of Donetsk.

On August 11, 2014, the ATO leadership issued an order, in execution of which the command of sector "B" developed a plan, one of the tasks of which was to block the city of Ilovaisk with the forces of the Armed Forces of Ukraine and clear it of illegal armed formations. Forces from separate battalions of the Ministry of Internal Affairs of Ukraine and the National Guard of Ukraine were involved in the execution of the combat task.

According to the specified order and plan, it was envisaged to take the city of Ilovaisk along with control over the northern outskirts of the city of Makiivka, which was supposed to lead to establishing control over supply routes and subsequently allow for encircling and liberating the city of Donetsk from terrorists.

In conducting the operation to defeat the main forces of IAF in the city of Ilovaisk and take it under control, units of the Armed Forces of Ukraine were also joined by units of the Ministry of Internal Affairs of Ukraine "Dnipro-1", "Shakhtarsk", "Azov", "Peacekeeper", "Kherson", "Sviatiz", "Ivano-Frankivsk", and the National Guard of Ukraine battalion "Donbas".

As a result of the execution of the combat task, with the support of the Armed Forces of Ukraine, the battalions of the Ministry of Internal Affairs of Ukraine and the National Guard of Ukraine managed to enter the city of Ilovaisk and secure themselves in the western part of the city. The other part of the city was held by IAF RF.
Considering the significant successes of our troops, in order to avoid the defeat of the mentioned terrorist organizations, in the third decade of August 2014, the leadership of the RF Armed Forces organized a direct invasion of regular Russian units into the territory of Donetsk region with simultaneous artillery shelling of the positions of the Armed Forces of Ukraine from Russia.
During the period from 8-23.08.2014, the positions of ATO forces in the directions of Savur-Mohyla - Uspenky - Amvrosiivka were systematically subjected to massive rocket and artillery shelling by RF Armed Forces personnel using MLRS BM-21 "Grad", BM-30 "Smerch", and 9P140 "Uragan", with increasing intensity.

The largest-scale invasion occurred on the night of August 23-24, 2014. The invading forces of the RF Armed Forces consisted of nine battalion tactical groups: 3,500 personnel; up to 60 tanks; up to 320 BMD (BMP); up to 60 guns; up to 45 mortars; 5 anti-tank missile systems, which entered the administrative territory of Ukraine in the area of the settlements of Pobieda - Berestove in the Starobeshivskyi district of Donetsk region, with a subsequent march towards the city of Ilovaisk in Donetsk region, where they broke through the units of the Armed Forces of Ukraine and other military formations.

In order to mislead and subsequently treacherously kill Ukrainian servicemen, tactical signs were pre-removed or masked on Russian military equipment, and identifying marks of Ukrainian units were applied, which is prohibited by Article 37 of the Additional Protocol to the Geneva Convention of 12.08.1949 (Protocol I) of 08.06.1977.

According to the data obtained by the investigation of the Security Service of Ukraine, intelligence agencies, and the Joint Staff of the ATO, the critical ratio of military forces of Ukraine in the area of the city of Ilovaisk with the units of the RF Armed Forces and representatives of the terrorist organizations "DPR", "LPR" was: personnel - 1 to 18; tanks - 1 to 11; armored vehicles - 1 to 16; artillery - 1 to 15; "Grads" - 1 to 24.

As a result of mass combat clashes between ATO forces and units of the RF Armed Forces, as well as simultaneous systematic mass rocket and artillery shelling of the positions of Ukrainian servicemen from the territory of the RF, some units of the Armed Forces of Ukraine were forced to leave sections of the state border at the line of Kuteinikove - Mokroye Lanchik, as well as positions in the areas of the settlements of Savur-Mohyla, Manuylivka, Berezove, south of Donetsk, which led to the weakening of the left flank of the ATO forces grouping and complicated the execution of tasks by units in the area of Ilovaisk. All this subsequently led to the encirclement of ATO forces in Ilovaisk.

As a result of prolonged powerful rocket and artillery strikes from the RF armed forces (including from Russian territory) on the units and subdivisions of ATO forces, as well as offensive actions of tactical groups of the RF Armed Forces in the Ilovaisk direction, conditions were created for the encirclement of certain units of sectors "D" and "B" and inflicting significant losses on them. The remaining units and subdivisions of sector "D", which were moving to reinforce the state border, suffered significant losses due to enemy shelling and were demoralized (leaving occupied positions, weapons, and military equipment without orders and chaotically retreating into the depths of the country).

On 24.08.2014, by directive of the ATO headquarters, Sector "D" was liquidated, part of the units was transferred to sector "B", and another part was withdrawn from the ATO zone for recovery measures. The combat actions of the Sector "D" units, if they had been combat-ready, could have significantly influenced the further execution of tasks by the grouping of troops in Sector "B".

Considering the real threat of invasion along the entire Russian-Ukrainian border, the Armed Forces of Ukraine actually did not have enough forces to increase the contingent of troops in the Donetsk direction while simultaneously ensuring the defense of other sections of the state border.

As a result of the sudden large-scale invasion on 24-25.08.2014 of regular units of the RF Armed Forces and their march towards the city of Ilovaisk, the forces and means of sectors "B" and "D" consisting of the respective units of the 51st separate mechanized brigade, 17th separate tank brigade, 93rd separate mechanized brigade, 55th separate artillery brigade, 91st separate operational support regiment, 121st separate communications brigade, 40th territorial defense battalion (hereinafter - TDB), 73rd marine special operations center, a combined unit of servicemen of the Armed Forces of Ukraine (Savur-Mohyla), units of the Ministry of Internal Affairs of Ukraine "Dnipro-1", "Peacekeeper", "Sviatiz", "Kherson", "Ivano-Frankivsk", "Azov", "Shakhtarsk", and the National Guard of Ukraine battalion "Donbas", which were in the area of the specified settlement, were encircled by significantly numerically superior units of the RF Armed Forces (the areas of the settlements of Pokrovka, Troitske - Khartsyzk, Zughres, Khartsyzk in Donetsk region), which invaded the territory of Ukraine (from the south and southwest) and IAF (from the west, north, and east).

To unblock Ilovaisk, a reserve was prepared from the 79th and 95th separate airborne brigades (hereinafter - oab) numbering up to 2,000 personnel. In this regard, the ATO Headquarters developed a plan on 27.08.2014, according to which the reserve troops of the ATO commander, in cooperation with the units of sector "B", were given a combat task to unblock the units of the Armed Forces of Ukraine, the Ministry of Internal Affairs of Ukraine, and the National Guard of Ukraine, which were in the city of Ilovaisk in Donetsk region and to complete the "clearing" of the city of Ilovaisk. The operation was planned to be carried out on 27-28.08.2014, but due to the recovery of the 79th airborne brigade, the operation was postponed to 01-02.09.2014.

During this period, the ATO and sector headquarters, in addition to the operation to withdraw the units of the Armed Forces of Ukraine, the battalions of the Ministry of Internal Affairs of Ukraine and the National Guard of Ukraine from encirclement in the area of the city of Ilovaisk, planned and conducted operations to hold strategically important facilities at the Luhansk airport, Novosvetlivka, Khrashchuvate, as well as carried out raid actions in the territory occupied by the enemy to liberate the settlements of Telmanove and Novoazovsk.
Convoys of sector "B" with ammunition, food, and water were unable to reach the units operating in Ilovaisk and around it. The number of wounded and killed was increasing, and there was no possibility to evacuate them due to the encirclement. The situation significantly worsened the moral and psychological state and combat spirit of the units.

As a result of powerful fire impact from the enemy on the battalions of the Ministry of Internal Affairs of Ukraine and the National Guard of Ukraine in the area of Ilovaisk, considering the criticality of the situation, the command of ATO forces determined the main task to preserve the lives of Ukrainian soldiers. For this purpose, negotiations began between the ATO commander Muzhenko V.M. and representatives of the General Staff of the RF Armed Forces (Deputy Chief of the General Staff of the RF Armed Forces Bogdanovsky M.V., Chief of the Main Operational Directorate of the General Staff of the RF Armed Forces Kartapolov A.V., Chief of the General Staff of the Ground Forces - First Deputy Commander of the Ground Forces Istrakov S.Yu., Chief of the Central Command Post of the General Staff of the RF Armed Forces Mizintsev E.M.), as well as at the level of the leadership of sector "B" and units of the RF Armed Forces, regarding the provision of guarantees of safe humanitarian corridors for the exit of Ukrainian servicemen from encirclement.
Only between ATO commander Muzhenko V.M. and Deputy Chief of the General Staff of the RF Armed Forces Bogdanovsky M.V., there were 12 phone calls during the period from 26-28.08.2014. During the negotiations, representatives of the RF Armed Forces constantly changed the time and conditions for exiting the encirclement and delayed time. As subsequent events showed, representatives of the RF Armed Forces deliberately delayed time to arrange tactically advantageous firing positions along the route of the ATO forces' exit from encirclement.

On 28.08.2014, representatives of the RF Armed Forces provided oral guarantees to the officials of the ATO leadership for a safe exit at dawn on 29.08.2014 from encirclement of Ukrainian servicemen in a column on military equipment in a marching (non-combat) order along the route from the area of the city of Ilovaisk to the line of Starobeshove - Novokaterynivka in the Starobeshivskyi district of Donetsk region.
An additional guarantee for a safe exit was to be the captured Russian servicemen, regarding whom there was an agreement to hand them over to representatives of the RF Armed Forces after exiting the encirclement.

On August 29, 2014, by direct order and command of the General Staff of the RF Armed Forces, Russian servicemen fired at close range on the columns of Ukrainian military personnel, along with captured Russian servicemen during the exit along the designated route as a humanitarian corridor for the personnel of the ATO forces in a marching (non-combat) order in the area of the settlements of Starobeshove, Chumaky, Novodvorske, Agronomichne, Mnohopyllya, Chervonosilske, Osikove, Novokaterynivka in Donetsk region.

Under these circumstances, a treacherous murder of 366 Ukrainian soldiers was committed, 429 were injured of varying degrees of severity, over 300 were captured (at this time, 41 people remain in captivity), more than 500 people went missing (at this time, 93 people remain missing), the Armed Forces of Ukraine suffered significant losses of weapons and military equipment amounting to nearly 300 million UAH.