Armenian and Azerbaijani forces are engaged in fighting over the Nagorno-Karabakh region, and at least one Azerbaijani helicopter has been downed.
Armenia says Azerbaijan started carrying out attacks on land and from the air, after which it declared martial law.
Azerbaijan, on the other hand, stated it was retaliating against Armenian attacks.
Both sides have reported civilian casualties.
The conflict, which has been ongoing for a long time, has intensified in recent months.
Turkish President Recep Tayyip Erdogan promised his country’s support to Azerbaijan and said Armenia is the biggest threat to peace and tranquillity in the region.
The Russian Foreign Ministry has called for an immediate cease-fire and for talks to stabilise the situation.
Both Armenia and Azerbaijan had been part of the former Soviet Union before it broke up in 1991.