MOSCOW — Heavy fighting broke out Saturday in Nagorno-Karabakh, an Armenian separatist enclave in Azerbaijan and a longtime ethnic tinderbox in the South Caucasus region.
More than 100 people were killed in the battle between Armenian and Azerbaijani forces, the Azerbaijan Defense Ministry said.
As the fighting escalated through the day it was unclear whether the use of tanks, artillery, and aircraft was merely a flare-up in a long conflict or the start of a new phase.
Artillery barrages began early Saturday, threatening a breakdown of a shaky 1994 truce agreement. Armenia and Azerbaijan, both former Soviet republics, blamed each other for the violence.
By evening, both sides spoke of dozens of dead, and Azerbaijan claimed that its military had advanced to capture territory, a move that seemed to bode ill for a quick resolution.
The ethnic war that began in the late Soviet period between Armenians and Azerbaijanis claimed more than 20,000 lives and ended in a cease-fire but no final settlement. The region became one of the so-called frozen conflict zones in the vast area of the former Soviet Union, with sporadic episodes of violence since the 1994 truce.
In response to the fighting, President Vladimir V. Putin of Russia called for an immediate cease-fire Saturday and urged both sides to show restraint. The Organization for Security and Cooperation in Europe, through the Minsk Group led by France, Russia, and the United States, condemned the violence.
The separatist government of Nagorno-Karabakh, whose principal backers are Armenia and Armenian diaspora groups in Southern California and elsewhere, characterized the fighting as the first time since 1994 that all types of heavy weaponry were being used along the front line.
Armenia’s Defense Ministry said Azerbaijan launched a surprise attack using tanks and aircraft around 2 a.m. after firing artillery barrages.
Azerbaijan’s Defense Ministry blamed the Armenian military for the fighting. It said that its soldiers and some residential areas near the front were struck by “intensive fire” early Saturday, and that its forces had taken “urgent measures” to respond.
Later Saturday, the ministry issued a statement saying it had recaptured “strategic heights” and a village to prevent attacks from those locations on its territory. It implied that Azerbaijan’s forces were moving beyond defensive positions and into Nagorno-Karabakh, a potentially destabilizing development in the volatile South Caucasus.
“There’s real doubt whether Putin will let that stand,” Cliff Kupchan, chairman of the Eurasia Group, a geopolitical risk analysis company, said in a telephone interview. “If we see this last a few days, then we have a new Nagorno-Karabakh war.”
The Azerbaijani statement said six tanks and 15 artillery pieces were destroyed Saturday. It said the more than 100 dead included 12 Azerbaijanis who had “become shahids,” meaning they died the death of Muslim martyrs.
The Nagorno-Karabakh military said it had shot down one of Azerbaijan’s helicopters, a claim Azerbaijan first denied and then confirmed. An official in Nagorno-Karabakh told Russian media that 40 to 50 Azerbaijani soldiers had been killed in the fighting.
Adding to the dangers of the ethnic hatreds between Christian Armenians and Muslim Azerbaijanis, the Nagorno-Karabakh region is buffeted by the combustible politics of the Middle East and the former Soviet republics.