The clashes over Nagorno-Karabakh are the heaviest seen since 2016 and have reignited concern over stability in the South Caucasus region, a corridor for pipelines carrying oil and gas to world markets.
The long-simmering conflict erupted anew on September 27 into the deadliest bouts of fighting in four years in the ethnic Armenian separatist enclave inside Azerbaijan.
The Nagorno-Karabakh conflict emerged during the breakup of the Soviet Union, when the region and seven adjacent districts of Azerbaijan were seized by Armenian-backed separatists who declared independence amid a 1988-94 conflict that killed at least 30,000 people and displaced hundreds of thousands.
Since a fragile, Russian-brokered truce in 1994, the region has been under the control of ethnic Armenian forces that Azerbaijan says include troops supplied by Armenia.