"For the moment, we have 49 (troops) killed and unfortunately it's not the final figure," Prime Minister Nikol Pashinyan told parliament. This death toll makes this the deadliest escalation since the two side fought a six-week war over Nagorno-Karabakh that claimed more than 6,500 lives.

Clashes erupted overnight along the volatile Azerbaijan-Armenia border near the disputed region of Nagorno-Karabakh, leaving troops dead on both sides, defence ministries in Baku and Yerevan said.

The latest flare-up risks marring ongoing talks between Armenia and Azerbaijan to sign a peace agreement.

It also risks stalling new efforts between Turkey and Armenia to strike a reconciliation agreement that would put an end to decades of hostile relations dating back to the genocide or Armenians by the Ottomans during World War I.

Armenia said that Azerbaijani forces "launched intensive shelling, with artillery and large-calibre firearms, against Armenian military positions in the direction of the cities of Goris, Sotk, and Jermuk" shortly after midnight.

But Azerbaijan's defence ministry accused Armenia of "large-scale subversive acts" near the districts of Dashkesan, Kelbajar and Lachin on the border, adding that its army positions "came under fire, including from trench mortars".

Turkey sides with Azerbaijan

Turkey firmly sided with its regional ally Azerbaijan, telling Armenia to "cease its provocations" against Baku.

"Armenia should cease its provocations and focus on peace negotiations and cooperation with Azerbaijan," Foreign Minister Mevlut Cavusoglu tweeted after a phone call with Azerbaijani counterpart Jeyhun Bayramov.

Turkey backed Baku in the 2020 conflict, supplying it with combat drones that helped Azerbaijan claw back large parts of the territory it lost in Nagorno-Karabakh in a brutal war that followed the Soviet Union's breakup in 1991.