Armenia’s defence ministry accused Azerbaijan’s armed forces of shooting down one of its military helicopters, reportedly killing all three of its crew members.
Azerbaijan said the aircraft had entered its airspace and was attacking its military positions, a charge Armenia denied
Armenia had been conducting training exercises near the border with Azerbaijan at the time of the incident.
The two countries fought a bloody war that ended in a 1994 cease-fire, but the pact has been shaky, with small outbreaks of fighting being reported occasionally.
The incident has stoked tensions between Armenia and oil-producing Azerbaijan.
The Azeri defence ministry said an army officer had been honoured for shooting down the aircraft.
Armenia has threatened to retaliate for the attack.