One person was killed and more than 30 injured after several rockets landed on residential areas of Ganja on Sunday, according to Azerbaijani officials. Ganja lies in the west of Azerbaijan to the north of Nagorno-Karabakh, close to crucial oil and gas pipelines that run from the capital Baku to Turkey. Azerbaijan and Armenia have been at loggerheads for more than three decades over the enclave inside Azerbaijan inhabited by Armenians. The recent fighting is the worst since the two sides fought a war when Nagorno-Karabakh broke away from Baku following the collapse of the Soviet Union.

The latest hostilities have ratcheted up tensions between Russia and Turkey, which on this occasion has openly supported Azerbaijan’s attempt to reclaim the territ ory. Moscow and Ankara are on opposites sides of the civil wars in Syria and Libya. Arayik Haru tyunyan, the Armenian leader of Nagorno-Karabakh, said in a tweet that he hadordered an artillery attack against Ganja’s military airport “as act of self-protection, in response to days-long deliberate shelling” of civilian areas in his region.

Stepanakert, the capital of Nagorno-Karabakh, has been hit by Azerbaijani shelling on a number of occasions since hostilities erupted on September 26. Armenian officials said the nearby town of Shusha was also hit on Sunday. The two sides have accused each other of using cluster munitions.

Azerbaijani officials denied that Ganja’s military airport had been hit despite Armenian claims the facility had been destroyed. The two sides have routinely disputed each other’s claimed battlefield successes during the recent fighting.