The Armenian military pledged on Saturday to use heavier artillery against Azerbaijani troops after accusing them of firing howitzer shells at Armenian soldiers for the first time since a Russian-brokered truce stopped the war in Nagorno-Karabakh in 1994.

Four of those soldiers were killed and as many as 16 others wounded in northeastern Karabakh on Friday evening.

According to Armenia’s Defense Ministry, they were struck by Azerbaijani artillery fire several kilometers away from the Armenian-Azerbaijani “line of contact” around the disputed territory. A ministry statement said the Azerbaijani army used Russian-made D-30 howitzers in the attack.

The 122-milimeter artillery systems have a firing range of 15 kilometers. Karabakh’s Armenian-backed army claimed that the Azerbaijani side fired a total of 30 D-30 rounds on Friday and early Saturday.

President Serzh Sarkisian pointed to the soldiers’ deaths and the fact that three Armenian civilians were killed by Azerbaijani shelling on Thursday as he vowed “punitive actions” against Baku on Friday. “We will certainly force Azerbaijan’s government to be accountable to its people for more suffering inflicted on them,” Sarkisian said at a meeting with senior officials in Yerevan.

The Defense Ministry elaborated on the promised retaliation in a special statement. “In order to silence the enemy, thwart its actions and thereby support the [Karabakh] peace process, from now on the Armenian Armed Forces will use adequate means of artillery and rocket fire, constantly targeting the sites of Azerbaijani troop deployments and movements, military hardware and personnel,” it said.

There was no immediate reaction to these statements from Baku. Earlier in the day, the Azerbaijani Defense Ministry said that its frontline units are “using more powerful weaponry to resolutely thwart any action by the enemy.”

Until last year ceasefire violations in the Karabakh conflict zone took the form of periodical exchanges of automatic and sniper fire between the two warring sides and overnight incursions by their commando units. Over the past year, the Armenian side has accused the Azerbaijani army of increasingly resorting to mortar fire during skirmishes. Baku says that the Armenians themselves are now using 60-milimeter and 82-milimeter mortars.

The use of heavier and more devastating artillery, if it becomes a regular occurrence, would mark a further escalation of the conflict and seriously complicate international mediators’ efforts to broker a peaceful settlement.

“The use of artillery by the Azerbaijani side … is yet another step towards full-scale hostilities,” warned the Armenian Defense Ministry.

Both the ministry and Sarkisian claimed that the Azerbaijani leadership has been emboldened by the international community’s reluctance to explicitly blame Baku for increased truce violations. Sarkisian said that Yerevan is now left with no choice but to ensure that “the adversary does not think that it has gotten away with its impudent behavior.”

“We are prepared to take up the gauntlet,” Deputy Foreign Minister Shavarsh Kocharian told reporters. “We know who we are dealing with. We have such experience.”