Azerbaijan sent troops backed by artillery strikes into Armenian-controlled Nagorno-Karabakh on Tuesday in an attempt to bring the breakaway region to heel by force, raising the threat of a new war with its neighbor Armenia.

Karabakh, a mountainous area in the volatile wider South Caucasus region, is internationally recognized as Azerbaijani territory. But part of it is run by separatist Armenian authorities who say the area is their ancestral homeland.

Karabakh has been at the center of two wars - the latest in 2020 - since the 1991 fall of the Soviet Union. U.S. Secretary of State Antony Blinken called on Azerbaijan to halt its operation immediately, saying it was worsening an already dire humanitarian situation in Karabakh - a reference to a lengthy de facto blockade of the region by Baku.

The European Union, France, and Germany also condemned Azerbaijan’s military action, calling on it to return to talks on the future of Karabakh with Armenia.

Loud and repeated shelling was audible from social media footage filmed on Tuesday in Stepanakert, the capital of Karabakh, called Khankendi by Azerbaijan.

Hikmet Hajiyev, foreign policy adviser to Azerbaijani President Ilham Aliyev, said Baku had deployed ground forces which he said had broken through Armenian lines in several places and achieved some of their main goals, something Armenian separatist forces denied.

A Baku defense ministry statement said Azerbaijani forces had so far seized more than 60 military posts and destroyed up to 20 military vehicles with other hardware.

Karabakh separatist authorities said 25 people had been killed, including two civilians, and 138 injured due to Baku’s military action. Inhabitants of some villages had been evacuated, they said.

Reuters could not verify either side’s assertions.

It was not clear whether Baku’s actions would trigger a full-scale conflict dragging in Armenia. But there were signs of political fallout in Yerevan where Armenian Prime Minister Nikol Pashinyan - viewed as too pro-Western by Russia, Armenia’s traditional supporter - spoke of calls for a coup against him.

Some Armenians gathered in Yerevan, the capital of Armenia, to demand action from the government amid reports of violent clashes between police and crowds which resulted in injuries on both sides.

The fighting in Karabakh could alter the geopolitical balance in the South Caucasus, which is crisscrossed with oil and gas pipelines, and where Russia - distracted by its own war in Ukraine - is seeking to preserve its influence in the face of greater activity from Turkey, which backs Azerbaijan.

Close a chapter

Azerbaijan’s Hajiyev said the army was using guided munitions against military targets to try to avoid collateral damage to civilians.

“The intention of Azerbaijan is to close a chapter of animosity and confrontation,” said Hajiyev.

“Enough is enough. We cannot tolerate any longer having such armed forces on our territory and also a structure which, on a daily basis, challenges the security and sovereignty of Azerbaijan.”

Azerbaijan’s defence ministry spoke in a statement of its intention to “disarm and secure the withdrawal of formations of Armenia’s armed forces from our territories, (and) neutralise their military infrastructure”.

It said it was acting to “restore the constitutional order of the Republic of Azerbaijan” and that civilians were free to leave by humanitarian corridors, including one to Armenia.

Nikol Pashinyan, Armenia’s prime minister, said the offer looked like another attempt by Baku to get Armenians to clear out of Karabakh as part of a campaign of “ethnic cleansing”, an accusation Baku denies.

Armenia, which had been holding peace talks with Azerbaijan, including on questions about Karabakh’s future, condemned Baku’s “full-scale aggression” against the people of Karabakh and accused Azerbaijan of shelling towns and villages.

Appeal for help

Armenia, which says its armed forces are not in Karabakh and that the situation on its own border with Azerbaijan is stable, called on members of the U.N. Security Council to help and for Russian peacekeepers on the ground to intervene.

Russia, which brokered a fragile ceasefire after a war in 2020 which saw Azerbaijan recapture swathes of land in and around Karabakh that it had lost in an earlier conflict in the 1990s, called for all sides to stop fighting.

Russia is in touch with both Azerbaijan and Armenia and has urged negotiations, Kremlin spokesman Dmitry Peskov said on Tuesday, adding that Moscow considered ensuring civilian safety the most important issue.

Armenia has accused Moscow of being too distracted by its own war in Ukraine to protect it and said Russian peacekeepers in Karabakh were failing to do their job. Protesters unhappy about what they saw as Moscow’s failure to stop Azerbaijan chanted anti-Russian slogans outside Russia’s embassy in Armenia on Tuesday evening, Russia’s state TASS news agency reported.

The United States was pursuing crisis diplomacy over what it believed was a particularly dangerous flare-up, U.S. officials said, saying Blinken was likely to get involved in the next 24 hours in trying to defuse the crisis.

France, which said it wanted a U.N. Security Council meeting on Thursday, said it was working with its partners to respond strongly and Germany said Azerbaijan had broken a promise not to resort to military action. Turkey said it supported Baku’s drive to preserve its territorial integrity.

Speaking inside Karabakh with artillery rumbling in the background, Ruben Vardanyan, a top official in Karabakh’s ethnic Armenian administration until February, appealed for Armenia to recognise Karabakh’s self-declared independence from Azerbaijan.

“A really serious situation has unfolded here,” Vardanyan said in a video clip. “Azerbaijan has started a full-scale military operation against 120,000 inhabitants, of which 30,000 are children, pregnant women and old people,” he said.