Joint Forces Operation (Ukraine)

Anti-Terrorist Operation Zone (Зона проведення антитерористичної операції), or ATO zone (Зона АТО), was a term used by the media, publicity, the government of Ukraine, and the OSCE and other foreign institutions to identify Ukrainian territory of the Donetsk and Luhansk regions (oblasts) under the control of Russian military forces and pro-Russian separatists. A significant part of ATO zone is considered temporarily occupied territory of Ukraine.

History
On 20 February 2018, Ukrainian President Petro Poroshenko changed the status of the ATO zone from an anti-terrorist operation to "taking measures to ensure national security and defense, and repulsing and deterring the armed aggression of the Russian Federation in Donetsk and Luhansk oblasts".

This allows the Ukrainian military to take charge of the zones instead of the Ukrainian secret service SBU. As such, the ATO was renamed to JFO zone (Joint Forces Operation (Операція об'єднаних сил, ООС).

Following the Russian invasion of Ukraine, out-of-service ATO veterans have repeatedly been the target of Russian forces, for example of the Redut PMC. According to captured fighters, with this they wanted to decrease the risk of them joining the defence of Ukraine. For this purpose, veterans were interrogated and tortured in order to find more, after which many were killed. Two Redut PMC fighters got convicted for committing such war crimes.

Military administrative division
The official borders of the ATO zone were defined with a list of localities and their geographical coordinates, approved in November 2014 by Ukraine's parliament, the Verkhovna Rada.

The zone is conditionally divided into five sectors A, B, C, D, and M.
 * Sector A – eastern and central parts of Luhansk Oblast
 * Sector B – central parts of Donetsk Oblast including Donetsk and Makiivka
 * Sector C – northern parts of Donetsk Oblast (cities Bakhmut and Debaltseve), and western parts of Luhansk Oblast
 * Sector D – southern parts of Luhansk Oblast and eastern parts of Donetsk Oblast (after the 2014 Russian invasion on August 24, all Ukrainian forces were withdrawn)
 * Sector M – southern parts of Donetsk Oblast (around Mariupol, hence the sector's identification)

Influence in culture and society
Since 28 December 2015, the song "Brattia Ukraintsi" (Brothers Ukrainians) is the official anthem of ATO.