The Armenian Defense Ministry’s press service said "Azerbaijani forces opened fire from mortars and large-caliber firearms at the eastern direction of the Armenian-Azerbaijani border."

Armenia's Defense Ministry said in a statement three died on the Armenian side as a result.

Armenian Prime Minister Nikol Pashinian said in a tweet that three of his troops had been killed in "an attack against Armenian independence, sovereignty and democracy."

"Withdrawal of Azerbaijani troops and deployment of an international observer mission on the Armenian territories affected by Azerbaijani occupation and bordering areas is an absolute necessity," he wrote.

The Armenian side resorted to retaliatory actions after the shooting started, Defense Ministry spokesman Aram Torosyan said.

The Defense Ministry of Azerbaijan blamed the Armenian side, saying it violated the cease-fire. According to Baku, one Azerbaijani soldier was wounded.

"All responsibility for the incident lies with the military and political leadership of Armenia," the Azerbaijani Defense Ministry said.

The ministry said despite the cease-fire agreement the Armenian armed forces opened fire on the units of the Azerbaijani Army around 6 p.m. local time in the Kalbajar region with different types of firearms.

The fighting threatens a fragile cease-fire agreement that ended the worst fighting between the two ex-Soviet Caucasus countries since a 2020 war over the breakaway region of Nagorno-Karabakh.

After a flare-up that killed more than 200 soldiers, the two sides on September 23 agreed to the Russia-brokered cease-fire to end the most recent hostilities.

Baku and Yerevan have been locked in a conflict over Nagorno-Karabakh for years. Armenian-backed separatists seized the mainly Armenian-populated region from Azerbaijan during a war in the early 1990s that killed some 30,000 people.

The two sides fought another war in 2020 that lasted six weeks before a Russia-brokered cease-fire, resulting in Armenia losing control over parts of the region, which is part of Azerbaijan, and seven adjacent districts.

Under the cease-fire Armenia ceded swaths of territory it had controlled for decades and Moscow deployed about 2,000 troops to the region to serve as peacekeepers.

With Moscow increasingly isolated following its invasion of Ukraine, the United States and the European Union have taken leading roles in mediating the Armenia-Azerbaijan normalization process.

Last week, the two countries' foreign ministers met in New York for talks arranged by U.S. Secretary of State Antony Blinken.

Earlier this year the EU led negotiations in Brussels between Azerbaijani President Ilham Aliyev and Pashinian at which they agreed to "advance discussions" on a future peace treaty.

They last met in Brussels on August 31, for talks mediated by European Council President Charles Michel.

The issue of ensuring a land link between Azerbaijan and its ally Ankara via Armenian territory has emerged as the primary sticking point.

With reporting by AFP and Reuters