"Operation Ring (Russian: Операция «Кольцо», Operatsia Koltso; Armenian: «Օղակ» գործողություն, Oghak gortsoğut'yun), known in Azerbaijan as the Chaykend Operation (Azerbaijani: Çaykənd əməliyyatı) was the codename for the May 1991 military operation conducted by Soviet Internal Security Forces and OMON units in the Armenian populated regions of Western Azerbaijan in the Lesser Caucasus mountains, the Shusha, Martakert and Hadrut regions of the Nagorno-Karabakh Autonomous Oblast, and along the northwestern border of the Armenian SSR in Noyemberyan, Goris and Tavush. Officially dubbed a "passport checking operation," the ostensible goal launched by the Soviet Union's internal and defense ministries was to disarm Armenian militia detachments that had been organized in "[illegally] armed formations."[1] The operation involved the use of ground troops who accompanied a complement of military vehicles, artillery and helicopter gunships to be used to root out the self-described Armenian fedayeen...."
https://en.wikipedia.org/wiki/Operation_Ring