TVER, Russia — Azerbaijan’s foreign ministry apologized on Monday for what it said was the accidental shooting down of a Russian military helicopter, killing two crew members in an incident that threatened to draw Russia more deeply into an already escalating war between Armenia and Azerbaijan.
Turkey, a member of the North Atlantic Treaty Organization, is backing Azerbaijan in the conflict, while Russia has a mutual defense treaty with Armenia. Both Russia and Turkey have denied any direct role in the fighting, and Russia has sought to broker a cease-fire. But the two countries are already at odds in wars in Syria and Libya, raising the risk that the fighting in the Caucasus could mushroom into a wider conflict.
The attack on the helicopter was the first publicly known instance of Russian soldiers dying in the war. It came a day after Azerbaijan claimed a tactical victory in the fighting with the capture of a mountaintop town. At least 1,000 soldiers and civilians have already died in the short, bloody conflict.
Russia’s Ministry of Defense said in a statement that its Mi-24 helicopter gunship was flying inside Armenia but close to the border with the Azerbaijani region of Nakhichevan when it was shot down by a shoulder-fired antiaircraft missile.
It said the helicopter was escorting a column of Russian military vehicles assigned to a Russian military base in Armenia, and the aircraft wreckage is on Armenian territory. Two Russian aviators died and a third was wounded, the statement said.
The Russian military issued a statement early Monday evening saying it was investigating who had fired the missile. The Azerbaijani apology followed quickly.
“The Azerbaijani side expresses its sincere condolences to the families of the dead crew members and wishes a quick recovery for the wounded,” the Azerbaijani Foreign Ministry said in a statement. It called the attack a “tragic incident.”
The statement said the helicopter had been flying low and in the dark, near Azerbaijani troops on high alert, in an area where Russian helicopters had not been seen before. “The decision was taken to open fire,” it said.
By late Monday, the Russian government had not responded. President Vladimir V. Putin has said the mutual defense pact with Armenia only applies to threats to Armenian territory.
Shortly after becoming independent of the Soviet Union, Armenia and Azerbaijan fought a war over a mountainous region, Nagorno-Karabakh, from 1992 to 1994, in which Armenian forces prevailed. The area is internationally recognized as part of Azerbaijan, but it has a majority Armenian population and declared independence from Azerbaijan.
Since that war, the enclave and some adjoining parts of Azerbaijan have been under Armenian control, though there has been repeated skirmishing along its borders.
Fierce fighting erupted in September, and Azerbaijan has reclaimed some of the territory it lost more than a quarter of a century ago.