Battles between Armenian and Azerbaijan forces over the disputed region of Nagorno-Karabakh have continued overnight, as international calls for calm after the heaviest fighting between the two sides in years grew.

The Armenian defence ministry on Monday morning reported fighting throughout the night, while Azerbaijan’s defence ministry said Armenian forces were shelling the town of Terter.

The clashes between the two former Soviet republics, which fought a war in the 1990s, were the latest flare-up of a long-running conflict over Nagorno-Karabakh, a breakaway region that is inside Azerbaijan but is run by ethnic Armenians.

Defence ministry officials in Nagorno-Karabakh said on Monday 15 more servicemen had died overnight, bringing their total military fatality count to 32 since clashes erupted on Sunday morning.

Both sides, meanwhile, reported civilian casualties.

Nagorno-Karabakh separatists said one Armenian woman and a child were killed, while Baku said that an Azerbaijani family of five died in shelling launched by Armenian separatists.

“We are tired of Azerbaijan’s threats, we will fight to the death to resolve the problem once and for all,” Artak Bagdasaryan, 36, told the AFP news agency in Yerevan, adding that he was waiting to be conscripted into the army.

Azerbaijan claimed it captured a strategic mountain in the region that helps control transport communications between Yerevan and the enclave.

The clashes prompted a flurry of diplomacy to reduce tension in a decades-old conflict amid fears the violence could spiral out of control.

“We are a step away from a large-scale war,” Olesya Vartanyan of the International Crisis Group told AFP.

“One of the main reasons for the current escalation is a lack of any proactive international mediation between the sides for weeks,” she added.

President Donald Trump said on Sunday the United States would seek to end the violence.

“We’re looking at it very strongly,” he told a news briefing. “We have a lot of good relationships in that area. We’ll see if we can stop it.”

The US State Department condemned the violence in a statement, calling for an immediate halt to hostilities and any rhetoric or other actions that could make the situation worse.

US Democratic presidential candidate and former Vice President Joe Biden said in a statement that hostilities could escalate into a wider conflict and urged the Trump administration to push for more observers along the ceasefire line and for Russia “to stop cynically providing arms to both sides”.

Nagorno-Karabakh broke away from Azerbaijan as the Soviet Union collapsed in 1991 after fighting that left 30,000 dead and forced many more from their homes.

Although a ceasefire was reached in 1994, Azerbaijan and Armenia frequently accuse each other of attacks around Nagorno-Karabakh and along the separate Azerbaijan-Armenia frontier.

International diplomacy

Armenia said Azerbaijani forces had attacked civilian targets including Nagorno-Karabakh’s capital, Stepanakert, and promised a “proportionate response”.

“We stay strong next to our army to protect our motherland from Azeri invasion,” Armenian Prime Minister Nikol Pashinyan wrote on Twitter.

Azerbaijan denied an Armenian defence ministry statement that said Azerbaijani helicopters and tanks had been destroyed, and accused Armenian forces of launching “deliberate and targeted” attacks along the front line.

“We defend our territory, our cause is right!” Azerbaijan’s President Ilham Aliyev said in an address to the nation, echoing the words of Joseph Stalin at the outbreak of World War II in Russia. “Karabakh is Azerbaijan,” he said.

Both Armenia and Nagorno-Karabakh declared martial law and military mobilisation. Azerbaijan imposed military rule and a curfew in large cities.

#NagornoKarabakh: no longer violations of ceasefire or border incidents. War is resuming. Time for Russia, France and US, individually and jointly, to stop it.

— Dmitri Trenin (@DmitriTrenin) September 27, 2020

Turkey, an Azerbaijan ally, said it was talking to members of the so-called Minsk Group, which mediates between Armenia and Azerbaijan. Russia, France and the US are co-presidents.

Russian President Vladimir Putin spoke by phone to Pashinyan but no details of the conversation were available, and Turkish President Recep Tayyip Erdogan spoke to Aliyev.

Erdogan, promising support for Azerbaijan, said Armenia was “the biggest threat to peace in the region” and called on “the entire world to stand with Azerbaijan in their battle against invasion and cruelty”.

Pashinyan hit back, accusing Turkey of “dangerous behaviour” and urging the international community to ensure Ankara does not get involved in the conflict.

UN Secretary-General Antonio Guterres said he was “extremely concerned” and called on the sides to stop fighting and return to talks.

The European Union, the Organization for Security and Cooperation in Europe and Pope Francis also urged both sides to stop military actions and return to negotiations.

At least 200 people were killed in a flare-up of the conflict between Armenia and Azerbaijan in April 2016. At least 16 people were killed in clashes in July.

Azerbaijan has pledged to take back the territory, by force if necessary, while Armenia has said it will do all it can to defend the area.