Clashes broke out between Azerbaijani forces and the Karabakh army on Wednesday, leaving at least three people dead.
The latest flare of violence has jeopardized a fragile truce in the region, with European leaders urging restraint.
Azerbaijan carries out 'retaliatory operation,' Karabakh army mobilizes
The Azerbaijani Ministry of Defense said one of its soldiers died following a "terrorist act" by "illegal military formations."
As a consequence, Baku said it carried out a "retaliatory operation," leading to an unspecified number of "illegal Armenian militants" being injured.
Baku also demanded the complete withdrawal of Armenian troops around Nagorno-Karabakh.
The Karabakh army, which is ethnically Armenian, said two of its soldiers were killed and 14 were wounded by Azerbaijani forces.
The enclave's separatist leader, Arayik Harutyunyan, announced a partial mobilization Wednesday, further escalating the crisis.
Armenia's foreign ministry called on the "international community to take measures to stop the aggressive actions and attitude of Azerbaijan."
Yerevan said Azerbaijan attacked areas which are patrolled by peacekeepers.
A spokesperson for EU foreign policy chief Josep Borrell urged an immediate end to Karabakh hostilities.
"It is essential to de-escalate, fully respect the cease-fire and return to the negotiating table to seek negotiated solutions," Borrell's spokesperson said.
Russia accuses Azerbaijan of violating cease-fire
Russia's Defense Ministry blamed Azerbaijan for breaking the cease-fire, which Moscow brokered in 2020.
"In the Saribaba area, the cease-fire regime was violated by the armed forces of Azerbaijan," the Russian ministry said in a statement. Moscow claimed it "was taking measures to stabilize the situation" with the help of Armenian and Azerbaijani representatives.
Armenia and Azerbaijan fought over Nagorno-Karabakh for six weeks in the fall of 2020 prior to the truce, with the conflict that year leaving over 6,500 people dead.
As part of the cease-fire, Armenia forfeited parts of Nagorno-Karabakh it controlled to Azerbaijan.
Despite the truce, sporadic clashes have persisted between the two sides, reducing the chances of a long-term peace agreement in the region.
