Azerbaijani and Armenian troops clashed early Tuesday, Russian news agencies reported, in a continuation of decades-old hostilities over the disputed territory of Nagorno-Karabakh.

Azerbaijani forces shelled Armenian troops at three points along the border around midnight. Azerbaijan said it was responding to an Armenian build-up of landmines and weapons near the border.

Armenia retaliated.

The region was under the control of Armenian separatists for nearly 30 years until Azerbaijan regained control of most of the territory in 2020 after a six-week war and a ceasefire agreement brokered by Russia.

Interfax reported that the Yerevan government said it would forge a cooperation agreement with Russia and appeal to the Collective Security Treaty Organization, a Russian-led security bloc, and the United Nations Security Council.

Besides Russian President Vladimir Putin, Armenian Prime Minister Nikol Pashinyan has called French President Emmanuel Macron and United States Secretary of State Anthony Blinken to discuss the situation.

Blinken called for an immediate end to hostilities in which each side blames the other.

As a result of intense shelling, Azerbaijan's armed forces suffered significant losses, according to the Ministry of Defense of Azerbaijan.

Azerbaijani statements said that Armenian forces were engaged in reconnaissance operations along the border, moved weapons into the area and conducted mining operations on Monday night.

Nagorno-Karabakh, long recognized internationally as Azerbaijan's territory, first erupted in the late 1980s when Armenian forces seized territory near Karabakh when both sides were under Soviet rule.

Azerbaijan regained those territories in the 2020 conflict. Thousands of residents returned to the homes they had fled under a Russian-brokered truce.

The leaders of the two countries have met several times to conclude a treaty intended to establish lasting peace.

49 Armenian soldiers killed in Azerbaijan attack

Azerbaijan's Foreign Ministry said in a statement that Armenian forces opened fire on military areas in three districts of the country and that Armenian separatists had planted mines in the areas. The Azerbaijani army suffered unspecified casualties. "It is only because of this that retaliatory measures have been taken," the statement said.

Armenian Prime Minister Nikol Pashinyan told parliament that Azerbaijani forces had attacked half a dozen points, Interfax news agency reported.

The Armenian Prime Minister said on Tuesday that 49 Armenian soldiers were killed in an attack carried out by the Azerbaijani army on Monday midnight. Azerbaijan responded that it was only retaliating against the attack by Armenia.