Armenia's military has mobilized in response to this.Armenia and Azerbaijan, two former Soviet republics in the Caucasus, have accused each other of initiating deadly clashes, the worst since 2016, that broke out on Sunday in their decades-long territorial dispute.
Ethnic Armenian separatists seized the Nagorno-Karabakh region from Baku in a 1990s war that claimed 30,000 lives. Since then, clashes have been a regular occurence between Azerbaijani troops and the rebels, but also between Baku and Yerevan.
On Sunday, Azerbaijan's defence ministry said it launched a "counter offensive to suppress Armenia's combat activity and ensure the safety of the population."
The enclave's separatist authorities claimed its troops shot down two Azerbaijani helicopters and three drones. Azerbaijan says it has just lost one helicopter.
Talks to resolve one of the worst conflicts to emerge from the 1991 collapse of the Soviet Union have been largely stalled since a 1994 ceasefire agreement.
France, Russia and the United States have mediated peace efforts as the "Minsk Group" but the last big push for a peace deal collapsed in 2010.
A fun wrinkle to this story is that you have Armenia, aligned with Russia, and Azerbaijan, aligned with Turkey. Both governments have threatened to get their respective regional power involved.
Azerbaijan has been getting whipped, despite having the technological advantage.