Armenia and Azerbaijan have declared martial law and mobilised their armed forces after clashes escalated over the disputed enclave of Nagorno-Karabakh, killing several people on Sunday. Both sides blamed each other for starting the fighting in the Caucasus Mountains, the latest flare-up in a decades-long conflict and the worst since a five-day war in 2016 in which more than 100   people died.

The region is an important corridor for European energy supplies via a pipeline that runs through Turkey, which sees itself as a “brother country” of Azerbaijan. Russia, the main mediator, has a mutual defence pact with Armenia and a military base in the country. Niko! Pashinyan, Armenia’s prime minister, said in an address to the nation that Azerbaijan had “declared war on the entire Armenian people once again” and said the “situation could go beyond the region’s borders and threaten international peace and stability”.

Ilham Aliyev, Azerbaijan ‘s president, said in a televised address to the nation on Sunday that thefighting “is a serious blow to the peace process,” according to Interfax. “Karaba kh is Azerbaijan, ” he said.”The enemy has tried to provoke us once again today, and I declare that our opponents will get the punishment they deserve.”

Armenia’s defence ministry said it shot down four Azeri helicopters and hit 10 tanks and 15 drones in response to an air offensive in Nagorno-Karabakh. The Armenian-backedgovernment ofNagorno-Karabakh said that 16 soldiers were killed and more than 100 were wounded, blaming Azerbaijan for shelling in the area. It added that two civilians were killed during the shelling and a further 30 were wounded.

Azerbaijan, which said 19 of its civilians were in the hospital, claimed to have recaptured several villages it lost in the war in 1993, though Armenia denied this. Azerbaijan’s defence ministry said it was taking “retaliatory measures” to protect civilians from “large-scale provocations” by Armenia in civilian areas near Nagorno-Karabakh that caused “serious” damage to infrastructure. It claimed to have destroyed 12 Armenian anti-aircraft systems while losing one Azeri helicopter.