Both countries' defense ministries are blaming each other for the deadly cross-border exchange. It is the most serious incident since they renewed their attempts at peace.
Armenia, on Tuesday, said four of its soldiers have been killed along the nation's heavily guarded border by Azerbaijani forces, even as the countries are involved in peace talks to end a 30-year-long conflict.
"Four were killed and one injured as a result of fire on Armenian positions from Azerbaijani troops," the Armenian defence ministry said in a statement.
Azerbaijan's border service responded to the statement, saying it had staged a "revenge operation" in retaliation for a "provocation" Armenian forces had committed the day before. Azerbaijan's Defense Ministry said Armenian forces had fired at Baku's positions along a northwestern section of the border.
Armenia has denied these claims.
The Kremlin on Tuesday called on Armenia and Azerbaijan to exercise restraint following the latest incident.
Russia — formally allied to Armenia but also has ties with Azerbaijan — has a contingent of peacekeepers deployed in the region, and its border guards patrol Armenia's frontiers.
Yerevan and Baku have fought two wars and seen three decades of conflict over the Nagorno-Karabakh region.
In September 2023, Azerbaijan reclaimed the disputed region in a lightning offensive against Armenian separatists who had controlled it since the collapse of the Soviet Union. It prompted a rapid exodus of almost all of the territory's Armenian inhabitants.