The OSCE Minsk Group -- co-chaired by France, Russia, and the US -- was formed in 1992 to find a peaceful solution to the conflict, but to no avail. A cease-fire, however, was agreed to in 1994.
Roughly 20% of Azerbaijan's territory has remained under illegal Armenian occupation for some three decades.
The two states agreed to a humanitarian cease-fire taking effect on Saturday for the exchange of prisoners and retrieval of bodies in Upper Karabakh.
The truce came after a trilateral meeting in Moscow on Friday among the foreign ministers of Russia, Azerbaijan and Armenia.