The announcement of ceasefire sparked protests in Armenia as the protesters stormed government buildings and the parliament.
Armenian Prime Minister Nikol Pashinyan called the decision to sign the agreement “incredibly painful” for himself and the people.
In Azerbaijan, however, people took to the streets to celebrate.
It follows six weeks of deadly fighting between Azerbaijani and Armenian forces.
The region is internationally recognized as Azerbaijani but has been run by ethnic Armenians since 1994.
A Russian-brokered truce was signed at the end of the conflict in the early 1990s but there was no peace deal.
Under the new deal struck by the leaders of Russia, Armenia and Azerbaijan, a ceasefire took effect in Nagorno-Karabakh on Tuesday, November 10.
The agreement allows Azerbaijan to hold onto portions of Nagorno-Karabakh seized by Armenian forces over the last several weeks of fighting.
Armenia must pull out from several nearby areas this month but can keep control of the rest of the region.
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