On September 27, Baku said that Armenia had shelled the Azerbaijani army’s positions and Yerevan, in turn, claimed that Azerbaijan’s Armed Forces had launched an offensive towards Nagorno-Karabakh, shelling regional settlements, including the capital, Stepanakert. Both parties reported casualties, including civilian casualties. The Armenian authorities declared martial law and announced a mobilization. Azerbaijan also declared martial law and announced a partial military mobilization. 

The conflict between Armenia and Azerbaijan over the highland region of Nagorno-Karabakh, a disputed territory that had been part of Azerbaijan before the Soviet Union break-up, but primarily populated by ethnic Armenians, broke out in February 1988 after the Nagorno-Karabakh Autonomous Region announced its withdrawal from the Azerbaijan Soviet Socialist Republic. In 1992-1994, tensions boiled over and exploded into large-scale military action for control over the enclave and seven adjacent territories after Azerbaijan lost control of them. Talks on the Nagorno-Karabakh settlement have been ongoing since 1992 under the OSCE Minsk Group, led by its three co-chairs - Russia, France and the United States.