Armenia has declared martial law and a total military mobilization following clashes with neighboring Azerbaijan over the breakaway region of Nagorno-Karabakh.
The incident has prompted calls from several world powers for an end to hostilities amid fears of instability in the South Caucasus - which serves as a corridor for pipelines transporting oil and gas to world markets.
[Armenian foreign ministry spokeswoman, Anna Naghdalyan, saying:] "Early in the morning, around 7 a.m. the Azerbaijani forces launched a large-scale aggression, including missile attacks..."
On Sunday (September 27) Armenia said Azerbaijan had carried out an air and artillery attack on Nagorno-Karabakh, but Azerbaijan said it had simply responded to Armenian shelling.
There were reports of civilian casualties on both sides.
Nagorno Karabakh is a mainly ethnic Armenian region that is internationally recognized as a part of Azerbaijan.
It declared independence in 1991, during the collapse of the Soviet Union, and the two countries have been at loggerheads ever since.
Authorities inside Nagorno Karabakh also declared martial law on Sunday, and mobilized the male population.
The two sides regularly accuse each of attacks and 200 people were killed when the conflict flared in 2016.
On Sunday, Turkey said majority Christian Armenia should immediately cease hostilities against mainly Muslim Azerbaijan while Russia's foreign ministry - a mediator in decades of conflict between the two sides - call for a cease fire and talks.
France said it was "extremely concerned" and said both sides should end hostilities.