Both Azeri and Armenian defense ministries accused each other of provoking the escalation. Azerbaijan said Armenian troops opened fire 127 times over 24 hours along the border. They were using mortars and heavy machine guns, the statement released on Saturday morning said.
Armenia said Azeri troops went on the offensive overnight and were using tanks artillery and military aircraft.
Militias in the unrecognized Karabakh republic, the focal point of the conflict, claimed they shot down two Azeri helicopter gunboats and a drone and destroyed two tanks. Azerbaijan has denied those reports.
Azerbaijan reported, “destroying a large number of enemy forces, hardware and military infrastructure” during the clashes. Armenia said Karabakh military “caused significant casualties and pushed the enemy back.”
Yerevan distinguishes its own armed forces from those of the breakaway republic, while Baku considers them all Armenian.
The two countries blamed each other for triggering the escalation.
“The responsibility for the situation is fully on Armenia, the aggressor and occupier nation,” the Azeri Foreign Ministry said in a statement. Armenia said it condemned the actions of the “Azerbaijan military along the engagement line with Nagorno Karabakh and the border with Armenia.” Both accused their rival of targeting civilians in Azerbaijan and Karabakh respectively.
Russian President Vladimir Putin has called on all sides in the conflict to immediately cease hostilities, the Kremlin spokesman said.
The Russian Foreign Ministry said Moscow was in contact with other members of the OSCE Minsk group, which is tasked with monitoring the Karabakh truce, and was closely watching the development of the situation.
Russian Defense Minister Sergey Shoigu held emergency phone talks with his Armenian and Azeri counterparts to discuss how the situation can be defused, the ministry said in a statement.
The two former soviet republics are locked in a decades-long conflict over Karabakh, a predominantly Armenian mountainous region that was part of Azerbaijan, but broke away in 1988.
The region declared independence in 1991, with a bloody three-year war following it. Russia brokered a ceasefire between Armenia and Azerbaijan in 1994, but the tensions have never actually stopped since then and there is occasional violence.
The mutual distrust between Armenia and Azerbaijan is rooted in a long history of ethnic and religious conflicts in the region as well as their participation in the rivalry of regional heavyweights – the Turks, the Russians and the Persians over the centuries.
Both nations had their first bid for statehood in the wake of the collapse of the Russian Empire in the early 20th century. Among other things their independence resulted in a war in 1918. When Moscow reinstated its control over the region, the conflict was swept under the rug, but never fully extinguished.
The current escalation comes amid the standoff between Russia and Turkey over the Syrian conflict. Ankara supports Azerbaijan, while Armenia is an ally of Moscow.