Clashes Erupt in Nagorno-Karabakh, Raising Fears of Another War

The leader of Armenia said on Tuesday that at least 49 of the country’s servicemen had died overnight in clashes with the Azerbaijani Army. It was the worst escalation of hostilities between two countries since the 2020 war over Nagorno-Karabakh, a disputed mountain enclave, and a threat to both a loyal Russian ally and a cease-fire that Russia brokered.

The clashes — which erupted early Tuesday, with both sides accusing each other of initiating them — resumed the decades-long armed conflict over Nagorno-Karabakh, which is internationally recognized as part of Azerbaijan but claims independence and is closely allied with Armenia.

The escalation between the two former Soviet states in the South Caucasus has heightened fears that Russia could find itself entangled in a second war in addition to its invasion of Ukraine. Some military analysts suggested that Azerbaijan may have been emboldened by Russia’s recent setbacks in northeastern Ukraine.

Speaking in Armenia’s Parliament, Prime Minister Nikol Pashinyan said that the intensity of hostilities had decreased but “attacks on one or two fronts from Azerbaijan continue,” according to a statement on the Parliament’s website.

Azerbaijan’s defense ministry accused Armenia of a number of “large-scale provocations” that forced it to retaliate, according to a statement on the ministry’s website. Mr. Pashinyan denied that his country had engaged in provocations and accused Azerbaijan of attacking the Armenian territories.

He convened Armenia’s Security Council which decided to turn to Russia for help. Russia and Armenia are part of the C.S.T.O., a Moscow-led military alliance whose charter stipulates that an attack against one member would be perceived as an aggression against all. Russia also has a military base in Armenia.

In Moscow, Russia’s foreign ministry called on both sides to exercise restraint and observe the agreements that ended the 2020 war, adding that it had brokered a renewed cease-fire to come into effect at 9 a.m. Wednesday.

In 2020, President Vladimir V. Putin of Russia helped sign a broad cease-fire after Azerbaijan went to war, recapturing some of the territory it had lost during another war that started during the collapse of the Soviet Union in the late 1980s.

For years, Moscow has been trying to strike a balance between Yerevan and Baku, but this has turned into an increasingly difficult task as the war in Ukraine forced the Kremlin to focus its attention and strength elsewhere.

As part of the agreement Mr. Putin sent about 2,000 peacekeeping troops to the area, demonstrating Russia’s role as a potent arbiter in the Caucasus region, which for decades has been plagued by conflicts and volatility.