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.

Nikol pashinyan, armenias 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 regions borders and threaten international peace and stability.

Ilham aliyev, azerbaijans president, said in a televised address to the nation on sunday that the fighting is a serious blow to the peace process, according to interfax. karabakh 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.

Nagorno-karabakh map

Armenias 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-backed government of nagorno-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 hospital, claimed to have recaptured several villages it lost in the war in 1993, though armenia denied this.

Azerbaijans 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.

The eu called for an immediate ceasefire and an urgent return to international negotiations to settle the long-running conflict, one of the most bloody that resulted from the collapse of the soviet union.

The flare-up pitches ankara and moscow on opposing sides of yet another conflict even as they have forged close co-operation on defence, energy and trade. the two nations, which share a suspicion of the west, have a complex relationship in which they have together on the civil wars in syria and libya despite backing rival parties in both countries.

Vladimir putin, russias president, told mr pashinyan that russia was deeply concerned about the clashes and urged both sides to take all necessary steps to prevent the conflict from escalating, and most importantly cease combat operations.

The turkish president, recep tayyip erdogan, called on armenians to take a stand against the countrys leaders, whom he said were using the nation's people like puppets and dragging them into a catastrophe. writing on twitter, he added: the turkish nation, as always, stands with its azeri brothers and sisters in every way possible.

Nagorno-karabakh, an ethnic armenian enclave of less than 150,000 people, lies within azerbaijans borders but broke away in the dying days of the soviet union and runs its affairs with political and military support from yerevan.

The war began in the early 1990s when ethnic armenian christians in nagorno-karabakh fought against mostly muslim azerbaijans control, and claimed thousands of lives before a ceasefire was signed in 1994.

Despite mediation from western powers and russia, armenia and azerbaijan have been unable to reach a full peace settlement and regularly renew skirmishes along the line of contact. at least 20 people died in clashes in july about 300km north of the enclave.

Tensions rose last week when mr aliyev claimed armenian forces were massing along the line of contact in preparation for war. armenia accused mr aliyev of fabricating the claim as a pretext to start military operations.

The attack was coming. there were numerous signals, all saw them and did nothing for weeks, olesya vartanyan, an analyst on the region for the international crisis group, wrote on twitter after the latest clashes. there was a need for a proactive international mediation. many found reasons to ok this attack. if they stay silent now, expect a real war.