Armenia, Azerbaijan, and Russia have signed an agreement to end military conflict over the disputed enclave of Nagorno-Karabakh.
Armenian Prime Minister Nikol Pashinyan called the deal “incredibly painful both for me and both for our people”.
It comes after six weeks of fighting between Azerbaijan and ethnic Armenians.
The region is internationally recognised as Azerbaijani, but has been run by ethnic Armenians since 1994.
In that year, a truce was signed after fighting but not a peace deal.
A number of ceasefire agreements have been brokered since fighting broke out again in September, but all of them have failed.
The new ceasefire agreement prompted anger in Armenia, as protesters stormed the parliament, beating up the speaker and reportedly looting the prime minister’s office.
The peace deal took effect on Tuesday from 01:00 local time (21:00 GMT Monday).
Under the new deal, Azerbaijan will hold on to areas of Nagorno-Karabakh that it has taken during the conflict. Armenia has also agreed to withdraw from several other adjacent areas over the next few weeks.
During a televised online address, Russia’s President Vladimir Putin said that Russian peacekeepers would be deployed to patrol frontlines. Russia’s defence ministry confirmed that 1,960 personnel would be involved and reports said planes had left an airbase at Ulyanovsk on Tuesday carrying peacekeepers and armoured personnel carriers to Karabakh.
Turkey will also take part in the peacekeeping process, according to Azerbaijan’s president, Ilham Aliyev, who joined President Putin during the address.
President Putin said the agreement would include an exchange of war prisoners, with “all economical and transport contacts to be unblocked.”
President Aliyev said the agreement was of “historic importance,” and amounted to a “capitulation” by Armenia.
Armenia’s prime minister said that his decision was based on “deep analyses of the combat situation and in discussion with best experts of the field”.
“This is not a victory but there is not defeat until you consider yourself defeated,” Mr Pashinyan said.
The Armenian leader in Nagorno-Karabakh, Arayik Harutyunyan, said a ceasefire was unavoidable after the loss of Karabakh’s second biggest town, Shusha (known as Shushi in Armenian).
Battles were already taking place on the outskirts of Karabakh’s main city, Stepanakert, and if the conflict had continued the whole of Karabakh would have been lost, he said on Facebook. “We would have far more losses,” he said.
In the Armenian capital Yerevan, a large crowd gathered to protest against the agreement, according to local media. They broke into parliament and government buildings, shouting “We will not give it up.”
Protesters ransacked the prime minister’s official residence and Mr Pashinyan said they “stole a computer, a clock, perfume, drivers licence and other items”.
The Armenians have steadily lost territory and significantly over the weekend Azerbaijani forces took over Shusha.
Azerbaijan has also admitted to mistakenly shooting down a Russian military helicopter over Armenia, killing two crew members and injuring a third.
It is unclear exactly how many have died. Both sides deny targeting civilians but accuse the other of doing so.
Nagorno-Karabakh’s authorities say nearly 1,200 of its defence forces have died in the fighting, and civilians have also been killed or injured.
Azerbaijan has not released its military casualty figures but has said more than 80 civilians have been killed in the fighting – including 21 in a missile strike on the town of Barda last month.
Russian President Vladimir Putin said last month that almost 5,000 people had been killed in the fighting.