Armenia declared martial law and total military mobilization after clashes with Azerbaijan over the Nagorno-Karabakh enclave, Armenian Prime Minister Nikol Pashinyan said Sunday.
"Get ready to defend our sacred homeland," Pashinyan said on Facebook.
Armenia and Azerbaijan report heavy fighting around the Nagorno-Karabakh on Sunday morning. The enclave has a majority Armenian population but is located entirely inside Azerbaijan.
Armenia accused neighboring Azerbaijan of attacks on civilian settlements in the disputed region.
"Our response will be proportionate, and the military-political leadership of Azerbaijan bears full responsibility for the situation," the Armenian Defense Ministry said in a statement.
The ministry also said its troops shot down two Azerbaijani military helicopters and three drones after Baku’s forces began bombing the breakaway enclave, including its capital, Stepanakert.
However, Azerbaijan's Defense Ministry said it had launched a military operation along the "contact line," between the two countries, “to suppress Armenia's combat activity and ensure the safety of the population."
The ministry confirmed the downing of only one Azerbaijani helicopter and said its crew had survived.
Armenian separatists seized Nagorno-Karabakh from Azerbaijan in a bloody war in the 1990s that killed 30,000 people.
Talks to resolve the conflict have been halted since a 1994 cease-fire agreement between Armenia and Azerbaijan.
Peace efforts mediated by France, Russia and the United States as the "Minsk Group" collapsed in 2010.