Heavy fighting has erupted between Armenia and Azerbaijan over the disputed Nagorno-Karabakh region, with both civilians and combatants killed.
Accusing Azerbaijan of air and artillery attacks, Armenia reported downing helicopters and destroying tanks, and declared martial law.
Azerbaijan said it had begun a counter-offensive in response to shelling.
The region is internationally recognised as part of Azerbaijan but controlled by ethnic Armenians.
They broke away in the dying years of the Soviet Union. Both Armenia and Azerbaijan were part of the communist state, which sought to suppress ethnic and religious differences.
Amid the clashes, Azerbaijani President Ilham Aliyev said he was confident of regaining control over the breakaway region.
Martial law has also been declared in some regions of Azerbaijan.
Learn more about Nagorno-Karabakh
- Armenia country profile
- Azerbaijan country profile
On Sunday, Turkey’s President Recep Tayyip Erdogan pledged support for Azerbaijan during the new crisis while Russia, traditionally seen as an ally of Armenia, called for an immediate ceasefire and talks to stabilise the situation.
France, which has a large Armenian community, called for an immediate ceasefire and dialogue.
Iran, which borders both Azerbaijan and Armenia, offered to broker peace talks.
Emboldened by Turkish support?
By Rayhan Demytrie, BBC Caucasus correspondent
Sunday’s fighting with the use of heavy weaponry along the line of control is the most serious escalation in recent years.
It is common in this decades-long conflict for both sides to accuse the other of firing the first shots and what we are seeing is not just military action but also an information war. It is difficult to independently verify official information.
Azerbaijan’s claim to have “liberated” territory controlled by Armenians has been denied by the Armenian authorities. Similarly, Armenia’s claims to have inflicted heavy losses on Azerbaijani forces have been dismissed by Baku. Moreover, the Azerbaijani authorities have restricted internet use inside the country, in particular access to social media.
Turkey’s emphatic support may embolden Azerbaijan. Back in August, the Azerbaijani defence minister said that with the help of the Turkish military Azerbaijan would fulfil its “sacred duty” – in other words, take back its lost territories.
How did the fighting spread?
Armenia’s defence ministry said an attack on civilian settlements in Nagorno-Karabakh, including the regional capital Stepanakert, began at 08:10 local time (04:10 GMT) on Sunday.
A woman and child were killed, officials said. The separatist authorities in Nagorno-Karabakh said 16 of their servicemen had died, with 100 injured.
Armenia said it had shot down two helicopters and three drones, as well as destroying three tanks.
Martial law is an emergency measure under which the military takes over the authority and functions of the civilian government.
“Get ready to defend our sacred homeland,” Armenian Prime Minister Nikol Pashinyan said after accusing Azerbaijan of “pre-planned aggression”.
Warning that the region was on the brink of a “large-scale war”, and accusing Turkey of “aggressive behaviour”, he urged the international community to unite to prevent any further destabilisation.
According to Azerbaijani prosecutors, five members of the same family were killed by Armenian shelling of one village in Azerbaijan.
Azerbaijan’s defence ministry confirmed the loss of one helicopter but said the crew had survived, and reported that 12 Armenian air defence systems had been destroyed. It denied other losses reported by Armenia.
President Aliyev said he had ordered a large-scale counter-offensive operation in response to Armenian army attacks.
“As a result of the counter-offensive operation, a number of Azerbaijani residential areas that were under occupation have been liberated,” he said in remarks broadcast on television.
“I am confident that our successful counter-offensive operation will put an end to the occupation, to the injustice, to the 30-year-long occupation.”
Armenia’s defence ministry denied any villages had been lost to Azerbaijan.
Nagorno-Karabakh – key facts
- A mountainous region of about 4,400 sq km (1,700 sq miles)
- Traditionally inhabited by Christian Armenians and Muslim Turks
- In Soviet times, it became an autonomous region within the republic of Azerbaijan
- Internationally recognised as part of Azerbaijan, but majority of population is ethnic Armenian
- An estimated one million people displaced by 1990s war, and about 30,000 killed
- Separatist forces captured some extra territory around the enclave in Azerbaijan in the 1990s war
- Stalemate has largely prevailed since a 1994 ceasefire
- Russia has traditionally been seen as an ally of the Armenians
President Erdogan called Armenia “the biggest threat to peace and tranquillity in the region”.
The Organisation for Security and Co-operation in Europe (OSCE) has long been trying to mediate a settlement of the conflict over Nagorno-Karabakh, with diplomats from France, Russia and the US – making up the OSCE Minsk Group – trying to build on a 1994 ceasefire.
Just how fragmented is the region?
Azerbaijanis are a predominantly Turkic people with whom Turkey has close ties, although unlike Turks, most Azerbaijanis are Shia, not Sunni, Muslims.
Turkey does not have relations with Armenia, a mainly Orthodox Christian country which has historically looked to Russia for support.
Iran, a mainly Shia state, has a large ethnic Azerbaijani community but maintains good relations with Russia. They and Turkey, a Nato member, back opposing sides in Syria’s ongoing civil war.
- Territorial disputes