MOSCOW — A long-simmering territorial dispute in the Caucasus region that reignited in recent days, with tanks, artillery helicopters and infantry engaged in combat, suggests that the two sides — Azerbaijan and Armenia — are girding for an extended conflict rather than the border skirmishes that they have engaged in over the years.
And what would seem to be a local war over a mountainous land of little strategic value is taking on greater importance because of its potential to draw in bigger powers like Russia and Turkey.
The fighting over the territory, known as the Nagorno-Karabakh enclave, escalated on Monday after breaking out over the weekend, with reports on both sides of rising numbers of wounded and dead.
The seemingly intractable tensions have their origins in the Soviet collapse 30 years ago when Karabakh, a predominantly ethnic Armenian enclave inside Azerbaijan, declared independence. Azerbaijan still claims the territory, and Armenia backs the enclave.
Russia has a mutual defense agreement with Armenia that could take effect if the fighting were to spread to Armenia proper, and Armenia has reported some shelling on its territory.
Turkey, a NATO member, is allied with Azerbaijan. On Monday, a national security adviser to President Recep Tayyip Erdogan of Turkey released a statement condemning Armenia. “We believe this conflict can be resolved through peaceful negotiations, but the Armenian side has shown no interest so far,” the statement said.
Urging Armenia to “stop violating international law,” the statement added: “We will continue to stand by the people of Azerbaijan and the government of Azerbaijan against any kind of aggression by Armenia or any other country.”
Russia and Turkey are already backing opposite sides in civil wars in Libya and Syria. At the same time, the countries kept up trade ties, cut natural gas deals and Turkey bought antiaircraft missiles from Russia, angering the United States. A Turkish news agency reported during the latest fighting that Turkish-made drones hit targets in Nagorno-Karabakh, raising the specter of a proxy battle in the enclave.
“Trespassing into former Soviet territory with arms is not something Russia will look kindly at,” Dmitry Trenin, director of the Moscow Carnegie Center, said in a telephone interview. “That could cross a red line” not passed before, he said.
Dmitri S. Peskov, the Kremlin spokesman, said on Monday that Russia was seeking to resolve the crisis and that “we are not talking now about military options.”
Over the years, the major powers — particularly Russia, which supplies the militaries of both sides and helps lead an international peace effort called the Minsk Process — have intervened to quell flare-ups.
Distracted by other issues like the pandemic, however — and a popular uprising in Belarus, another former Soviet state — international mediators missed warning signs in the Caucasus conflict, analysts say. Foreign leaders have called for a quick cease-fire, but both sides seem to be settling in for a long fight.
“All the signals were in place, everything was telling that escalation was coming,” Olesya Vartanyan, a senior analyst of the Caucasus at the International Crisis Group, said in a telephone interview. “And there was diplomatic silence.”
Virus travel restrictions, she noted, had prevented traditional shuttle diplomacy over the summer. “This is a perfect time” to start a war, Ms. Vartanyan said.
Azerbaijan’s president, Ilham Aliyev, ordered a partial mobilization of reserves and the country’s military on Monday, and, in the clearest terms yet, stated a goal of seizing territory. Armenia had earlier called up reserves.
The international airport in Baku, the Azerbaijani capital, canceled flights on Monday, while the authorities in Armenia announced a counteroffensive and said that fighting had intensified.
How the fighting began on Sunday morning is contested. Azerbaijan says Armenia fired artillery across the border, while Armenia says it was victim of an unprovoked attack.
Azerbaijan’s military issued a statement on Monday saying that its objectives were to shift the status quo by seizing territory from the enclave. “Azerbaijani units carry out combat operations to destroy the enemy and liberate our occupied lands,” the statement said.
President Aliyev said on Sunday that his military intended to target only the enclave, not Armenia.
Azerbaijan’s state news agency quoted a general, Mayis Barkhudarov, laying out the goals more graphically. “The Army Corps under my command will fight to the last drop of blood to completely destroy the enemy and win,” the state news agency quoted General Barkhudarov as saying.
The authorities in the Karabakh government, which is not recognized by other countries, said on Monday that they had recaptured lost positions in fighting overnight.
Both sides have offered high estimates for the others’ casualties, though these are typically exaggerated. Azerbaijan said it had killed 500 Armenian soldiers, while Armenia said it had killed 200 Azerbaijani soldiers. The Armenian military released a more credible figure for its own losses of 31 dead.
A previous bout of fighting in the area in 2016 killed about 200 soldiers on both sides, but quickly ended in a settlement negotiated by Russia.
Regional analysts have raised concerns about a small but real possibility that other countries could be drawn into the conflict. A war in Nagorno-Karabakh that ended in a cease-fire in 1994 was among the most vicious of the early post-Soviet conflicts. Three states — Russia, the United States and France — agreed to mediate the truce in the Minsk Process.
The hostilities erupted in the middle of the United Nations General Assembly’s annual meeting, held virtually this year, and amounted to a slap at entreaties by Secretary General António Guterres for a cease-fire to all violent conflicts, to help countries focus on the coronavirus pandemic.
Mr. Guterres issued a statement Sunday urging Armenia and Azerbaijan to stop fighting immediately and “return to meaningful negotiations” under the Minsk Process. His spokesman, Stéphane Dujarric, said Monday that Mr. Guterres was speaking by phone with the leaders of both countries.
“We’re talking about a conflict and exchange of fire that is ongoing,” Mr. Dujarric said, “and it’s an appeal for a cease-fire, for meaningful dialogue to resume without preconditions and without delay.”
Carlotta Gall contributed reporting from Istanbul.