Armenia and Azerbaijan said on Friday that they had sustained casualties in fighting around their common border, northwest of the breakaway region of Nagorno-Karabakh.

Armenia's Defence Ministry said two of its servicemen had been killed and another wounded in shelling near the border villages of Sotk and Norabak. Azerbaijan said Armenia had struck its positions across the border in the Kalbajar region using drones, wounding three servicemen.

"[Russia has shown an] absolute indifference to the aggression against the sovereign territory of the Republic of Armenia"

Armenian Foreign Ministry

The incident came a day after Armenia accused treaty ally Russia of "absolute indifference" towards attacks on its territory.

Armenia accused Azerbaijan of massing forces close to the border, and striking its positions using drones, mortars, and small arms fire. Azerbaijan denied gathering forces, but said it was taking "retaliatory measures."

Reuters was unable to verify the reports.

Nagorno-Karabakh, internationally recognized as part of Azerbaijan but inhabited primarily by ethnic Armenians, has been a source of conflict between the two Caucasus neighbors since before the collapse of the Soviet Union in 1991, and between ethnic Armenians and Turkic Azeris for well over a century.

Despite sporadic discussions on a peace deal to agree on borders, settle differences over the enclave, and unfreeze relations, tensions remain high and skirmishes along the shared border are a regular occurrence. Two days of clashes in September last year saw around 300 servicemen killed on both sides.

Continued fighting, along with a months-long blockade of Karabakh by Azerbaijan, have strained once warm relations between Armenia and Russia, which is Yerevan's traditional ally, and which has a peacekeeping contingent in Karabakh.

In a statement on Thursday, Armenia's Foreign Ministry accused Russia of "absolute indifference to the aggression against the sovereign territory of the Republic of Armenia," and of using a "false excuse" to avoid supporting Armenia.

In recent months, Russia has publicly backed Azerbaijan's claim to Nagorno-Karabakh and blamed Armenia for the ongoing blockade of separatist-held Karabakh.