Nagorno-Karabakh is internationally recognized as Azerbaijani territory but split up in 1991 and is ruled by ethnic Armenians.
The Armenian Defense Ministry reported fighting throughout Sunday night, while the Azerbaijani Defense Ministry said Armenian forces were bombing the town of Terter.
The worst skirmishes since 2016 have raised the specter of a new war between former Soviet rivals, locked since the early 1990s in a stalemate over the breakaway region of Nagorno-Karabakh backed by Armenia.
Seventeen Armenian separatist fighters were killed and more than 100 wounded in the fighting, Karabakh President Arayik Harutyunyan said on Sunday, acknowledging that his forces had “lost their positions”. Both sides also reported civilian casualties.
Karabakh separatists said an Armenian woman and a child were killed, while Baku said an Azerbaijani family of five died in bombings by Armenian separatists.
Azerbaijan claimed to have captured a strategic mountain in Karabakh that helps control transport links between Yerevan and the landlocked enclave inside Azerbaijan.
Armenian Defense Ministry spokesman Artsrun Hovhannisyan said in turn that the Karabakh rebel forces killed “some 200 Azerbaijani soldiers and destroyed 30 enemy artillery units and 20 drones”.
The fighting between Muslim Azerbaijan and predominantly Christian Armenia has threatened to confuse regional actors, Russia and Turkey, with Armenian Prime Minister Nikol Pashinyan calling on world powers to prevent Ankara’s involvement.
“We are on the brink of a full-scale war in the South Caucasus,” Pashinyan said.
France, Germany, Italy and the European Union quickly demanded an “immediate ceasefire” as Pope Francis prayed for peace.
The President of France, Emmanuel Macron, expressed his “deep concern” and “strongly called for an immediate end to hostilities”.
UN Secretary General Antonio Guterres said he was “extremely concerned” and urged the parties to stop the fighting and resume talks.
The US State Department said it had contacted the two countries and called on them to “use the existing direct communication links between them to avoid further escalation.”
Russian President Vladimir Putin discussed the military outbreak with Pashinyan and called for “an end to hostilities”.
But Azerbaijan’s ally Turkey blamed Yerevan for the outbreak and pledged Baku “full support”.
“The Turkish people will support our Azerbaijani brothers with all our means, as always,” wrote Turkish President Recep Tayyip Erdogan.
Karabakh President Harutyunyan said Turkey was providing mercenaries and fighter jets for the fight, suggesting that “the war has already … [gone] beyond the limits of a Karabakh-Azerbaijan conflict ”.
Azerbaijan has accused Armenian forces of violating a ceasefire, claiming to have launched a counteroffensive to “ensure the safety of the population” using tanks, artillery missiles, fighter jets and guns. drones.
In a televised address to the nation earlier on Sunday, Azerbaijani President Ilham Aliyev pledged victory over Armenian forces.
“Our cause is just and we will win,” he said, echoing a famous quote from Soviet dictator Joseph Stalin during the outbreak of World War II in Russia.
“Karabakh is Azerbaijan.”
Armenia and Karabakh declared martial law and military mobilization. Azerbaijan imposed a military regime and a curfew in the big cities.
Armenia said Azerbaijan attacked civilian settlements in Nagorno-Karabakh, including the main town, Stepanakert.
Azerbaijan’s Foreign Ministry said there were reports of deaths and injuries. “Considerable damage has been inflicted on many homes and civilian infrastructure,” he said.
Ethnic Armenian separatists seized the Nagorno-Karabakh region of Baku in a war in the 1990s that left 30,000 dead.
Talks to resolve one of the worst conflicts to emerge from the collapse of the Soviet Union in 1991 have largely been stalled since a 1994 ceasefire agreement.
France, Russia and the United States negotiated the peace efforts as a “Minsk group”, but the last big push for a peace deal collapsed in 2010.