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 follows 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.
A Russian-brokered truce was signed at the end of the war in the early 1990s but there was no peace deal.
Although both sides took steps to reduce tensions last year, fighting erupted at the end of September and several attempts to end the conflict 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.
What has been agreed?
The peace deal, which was signed by Russian President Vladimir Putin, Azerbaijani President Ilham Aliyev and Armenia's prime minister, took effect on Tuesday from 01:00 local time (21:00 GMT Monday).
Under the 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.
The BBC's Orla Guerin in Baku says that, overall, the deal should be read as a victory for Azerbaijan and a defeat for Armenia.
During a televised online address, President Putin said that Russian peacekeepers would be deployed to patrol the front line.
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. Part of their role will be to guard the "Lachin corridor", which links the Karabakh capital, Stepanakert, to Armenia.
Turkey will also take part in the peacekeeping process, according to Azerbaijan's president, who joined President Putin during the address.
