Caucasus warfare prompts EU alarm

Both sides accused each other of firing first, with no international monitors on the ground to verify claims.

They also imposed martial law and hardened their rhetoric.

"We defend our territory, our cause is right", Azerbaijan's president, Ilham Aliyev, said on TV.

"We stay strong next to our army to protect our motherland from Azeri invasion," Armenian prime minister Nikol Pashinyan said.

Sunday's fighting was the most intense in the past five years in a long-standing ethnic conflict over Nagorno-Karabakh, an Armenia-controlled enclave in Azerbaijan.

Clashes in July also killed 16 people and minor skirmishes claim lives almost every year, even though full-scale war ended in 1994.

For its part, Turkey, Azerbaijan's ally, also turned up the heat by threatening military intervention.

"Turkey fully supports Azerbaijan with unwavering solidarity. We will stand by Azerbaijan whichever way it prefers," the Turkish foreign ministry said on Sunday.

And Russia, the regional superpower, which has a defence pact with Armenia - the Collective Security Treaty Organisation (CSTO) - called for a ceasefire.

"All necessary efforts must be taken now to avoid further escalation of the conflict, key being a halt in military actions," the Kremlin said after Russian president Vladimir Putin spoke with Pashinyan by phone.

The threat of spiralling hostilities alarmed Armenia, however.

"I call on the international community to use all of its influence to halt any possible interference by Turkey, which will ultimately destabilise the situation in the region. This is fraught with the most devastating consequences," Pashinyan said.

It also alarmed Dmitri Trenin, the director of the Carnegie Moscow Centre, a think-tank.

"[These are] no longer violations of ceasefire or border incidents. War is resuming. Time for Russia, France, and US, individually and jointly, to stop it," Trenin said.

"Turkey's invasion of Armenia would activate the CSTO, which in turn might activate the North Atlantic one [Nato]. Scary," he added.

For their part, EU countries joined Russia in urging de-escalation.

"I call on parties to ... immediately stop all acts of fighting, especially the shelling of villages," German foreign minister Heiko Maas said out of Berlin.

"Hostilities in Nagorno-Karabakh must stop immediately. Extremely concerned about reports of civilian casualties," Dutch foreign minister Stef Blok said in The Hague.

Nato and the EU institutions also spoke out from Brussels.

"Nato is deeply concerned by reports of large-scale military hostilities," its spokesman said on Sunday.

"The European Union calls for an immediate cessation of hostilities," its foreign service said.

The South Caucasus is an important oil and gas transit route to Europe, but Western states have little leverage in the region.

France and the US are members of a diplomatic peace club called the "Minsk Group", created by the Organisation for Security and Cooperation in Europe.

But Russia has blocked EU efforts to build closer ties with Armenia and it has occupied parts of Georgia, while Azerbaijan, a petro-dictatorship, has shown little interest in EU assimilation.