Armenia has asked Russia to help defend its territorial sovereignty against Azerbaijan after a reported heavy border clash, Russia's TASS news agency said on Tuesday.
Tensions between Yerevan and Baku remain high after a 44-day war last year between ethnic Armenian forces and the Azeri army, backed by Turkey, that killed at least 6,500 people and ended in a decisive victory for Azerbaijan.
The Azeri defense ministry earlier on Tuesday spoke of what it said was a tense situation on the border with Armenia where it said a military operation was underway.
It said Armenian forces were shelling Azeri army positions with artillery and mortar fire.
The Armenian defense ministry was cited by Russian news agencies as saying in a statement that Azerbaijan was using artillery, small arms and armor in ongoing battles.
TASS said four Armenian soldiers had been wounded.
"Since Azerbaijan has attacked Armenia's sovereign territory we are asking Russia to defend Armenia's territorial integrity based on an existing 1987 (mutual defense) agreement between our countries," Interfax cited Armen Grigoryan, the secretary of Armenia's Security Council, as saying.
Russia has a military base in Armenia as well as a peacekeeping force in the Nagorno-Karabakh enclave where last year's war unfolded.
There was no immediate response from Russia to the Armenian appeal.