Azerbaijan on Tuesday launched a military operation against the breakaway Nagorno-Karabakh region, warning it would "continue until the end" in the territory, over which it has fought two wars with neighbouring Armenia.
The latest flare-up in violence came as Russia, the traditional power broker in the region, was bogged down in its invasion of Ukraine.
Fears of a fresh war in the volatile Caucasus region have been growing recently, with Armenia accusing Azerbaijan of a troop build-up around the disputed Armenian-majority territory.
Separatists said Azerbaijan was using artillery, combat aircraft and attack drones and Armenian Prime Minister Nikol Pashinyan called it a "ground offensive".
Blasts rocked the separatist stronghold Stepanakert earlier on Tuesday and hours later, an AFP journalist in the town said the shelling was "continuing".
Azerbaijan's defence ministry said it had taken control of more than 60 military positions during "localised anti-terrorist measures".
Armenian separatists said on social media that "fighting continues along the entire line of contact" and that Azerbaijani forces were "trying to advance" into the territory.
The separatists said 25 people, including at least five civilians, were killed, 80 more were wounded, and six villages had been evacuated.
Baku's presidency urged Karabakh separatists to lay down their arms and offered talks in the town of Yevlakh.
"Illegal Armenian armed forces must raise the white flag," it said. "Otherwise, the anti-terrorist measures will continue until the end."
Protests in Armenian capital
The ex-Soviet Caucasus rivals have been locked in a decades-long dispute over Karabakh, with large-scale hostilities breaking out in the 1990s and in 2020.
The latest flare-up raised fears that the unrest could destabilise the volatile region.
As angry protesters clashed with police in Armenia's capital Yerevan, calling on Pashinyan to resign, the country's security council warned of large-scale unrest.
"There is currently a real danger of mass turmoil in the Republic of Armenia," it said in a statement, vowing to take "effective measures" to maintain constitutional order.
The Armenian health ministry said that both police and civilians had sought medical help and some were hospitalised, without providing further details.
In a televised address, Pashinyan warned: "We must not allow certain people, certain forces to deal a blow to the Armenian state.
"There are already calls, coming from different places, to stage a coup in Armenia," he said.
Accusing Azerbaijan of engaging in "ethnic cleansing of Karabakh Armenians", Pashinyan said the Armenian army was not involved in the fighting and the situation on the border between Armenia and Azerbaijan was "stable".
He urged Russia and the UN to "take steps" and spoke on the phone to US Secretary of State Antony Blinken and French President Emmanuel Macron.
In separate statements, Blinken and Macron called on Baku to "immediately" halt its offensive.
Turkey says operation 'necessary'
Armenia's foreign ministry condemned Azerbaijani "aggression" aimed at completing "its policy of ethnic cleansing" and called on Russian peacekeepers stationed in the region to "take clear and unequivocal steps to stop" the fighting.
Azerbaijan justified its operation, citing "systematic" shelling by Armenian-backed forces and accusing them of carrying out "reconnaissance activities" and fortifying defensive positions, accusing separatists of "a high level of combat readiness".
Russia and Turkey, which oversee a fragile peacekeeping mission in Nagorno-Karabakh, had been informed about the operation, Baku said.
Turkey, a historic ally of predominantly Muslim Azerbaijan that views mostly Christian Armenia as one of its main regional rivals, called the operation "justified", while urging "comprehensive negotiations".
Moscow's foreign ministry spokeswoman Maria Zakharova said it was given "minutes'" notice of the start of Azerbaijan's operation.
Kremlin spokesman Dmitry Peskov said Russia was "concerned" and was working to get the two countries to negotiate.
Armenian separatists blamed international inaction for the fresh fighting.
"By ignoring warnings about Azerbaijan's criminal intentions and refusing to act accordingly, all the responsible international actors failed to prevent yet another Azerbaijani (act of) aggression" against Nagorno-Karabakh, they said in a statement.
France called for the Security Council to meet on the crisis, which comes as leaders gather for the annual General Assembly.
This operation is "illegal, unjustifiable and unacceptable," French Foreign Minister Catherine Colonna told reporters.
The fighting erupted just hours after Azerbaijan said four police officers and two civilians were killed in mine blasts in Nagorno-Karabakh, with authorities blaming separatists.
The deaths at dawn came after Armenian separatists said they had reached an agreement with Azerbaijani authorities to resume aid deliveries to Karabakh.
When the Soviet Union collapsed in 1991, ethnic Armenian separatists in Karabakh broke away from Azerbaijan.
The ensuing conflict claimed some 30,000 lives.
A six-week war in 2020 saw Armenia cede swathes of territory it had controlled since the 1990s.
(FRANCE 24 with AFP)
