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 northern regions (Shahumyan, Shusha, Martakert and Hadrut) of Nagorno-Karabakh Autonomous Oblast of the Azerbaijan SSR and in a number of bordering regions of the Armenian SSR (Noyemberyan, Goris and Tavush).