Clashes erupted between Azerbaijani and Armenian troops, with each side blaming the other for the outbreak in fighting, Russian news agencies reported early on Tuesday.
The Azerbaijani defense ministry claimed that the Armenian military engaged in wide-scale provocations near the Dashkasan, Kalbajar and Lachin regions and the "sabotage groups of the Armenian military" had laid mines on land and roads used by the Azerbaijani military.
"Several positions, shelters and reinforced points of the Azerbaijan armed forces ... came under intense shelling from weapons of various calibers, including mortars, by units of the Armenian army," the ministry said in a statement.
The Armenian defense ministry said that the Azerbaijani military fired at the territory of Armenia on Tuesday night using artillery and drones, leading to injuries and casualties.
Armenian Prime Minister Nikol Pashinyan has held phone talks with Russian President Vladimir Putin, French President Emmanuel Macron respectively on the situation.
Armenian government said it would invoke a cooperation agreement with Russia and appeal to the Collective Security Treaty Organization, as well as the United Nations Security Council, Interfax reported.
Pashinyan also discussed the situation with U.S. Secretary of State Antony Blinken in a phone call.
"As we have long made clear, there can be no military solution to the conflict," Blinken said in a statement. "We urge an end to any military hostilities immediately."
Armenia and Azerbaijan have been at loggerheads over the mountainous region of Nagorno-Karabakh since 1988. Peace talks have been held since 1994, when a ceasefire was agreed, but there have been sporadic minor clashes since then.
(With input from agencies)
(Cover: A picture taken on November 30, 2020 shows a destroyed Armenian military hardware. /AFP)