Armenia said on Tuesday that two of its soldiers had been killed by Azerbaijani fire along the heavily militarized border, the first fatal incident since the two sides last year began negotiating a deal to end more than 30 years of intermittent war.

Armenia’s Defense Ministry said in a statement posted on the Telegram messaging app that two of its soldiers had been killed and several more wounded at a combat post near the southern Armenian village of Nerkin Hand.

Azerbaijan’s border service said in a statement that it staged a “a revenge operation” in retaliation for a “provocation” it said Armenian forces had committed the day before.

It said that further “provocations” would be met with “more serious and decisive measures from now on.”

“The military and political leadership of Armenia is fully responsible for the incident.”

Azerbaijan’s Defense Ministry said that Armenian forces Monday evening fired at Baku’s positions along a northwestern section of the border, around 300 kilometers from Nerkin Hand. Armenia’s Defense Ministry denied that such an incident took place.

Armenia and Azerbaijan have been locked in conflict for over three decades over Nagorno-Karabakh.

Azerbaijan in September retook Karabakh in a lightning offensive, prompting a rapid exodus of almost all of the territory’s Armenian inhabitants, and a renewed push from both sides for a treaty to formally end the conflict.

Although fatal exchanges of fire between Armenia and Azerbaijan have been common for decades, the border had become more peaceful since the start of talks, with little serious fighting since the collapse of Karabakh in September 2023.

The peace talks have in recent months appeared to stagnate, with both sides accusing the other of sabotaging the diplomatic process.