Fighting between Armenia and Azerbaijan broke out on Sunday over the separatist region of Nagorno-Karabakh.
Armenian authorities said that at least 16 people had been killed and some 100 wounded, said euronews.com.
Nagorno-Karabakh is an ethnically Armenian enclave within Azerbaijan that has been out of Azerbaijan’s control since the end of a war in 1994.
Both sides have a heavy military presence along a demilitarised zone separating the region from the rest of Azerbaijan.
Armenia said the fighting Sunday began with an Azerbaijani attack, but Azerbaijan said the Armenian side attacked and that Azerbaijan launched a counteroffensive.
Armenian Prime Minister Nikol Pashinyan said the “aggression was pre-planned and constitutes large-scale provocation against regional peace & security.”
Both countries have declared martial law.
The Armenian Defence Ministry said two Azerbaijani helicopters were shot down and that Armenian forces hit three Azerbaijani tanks earlier in the day.
The news was harshly received in Turkey.
Turkey’s ruling party spokesman Omer Celik tweeted: “We vehemently condemn Armenia’s attack on Azerbaijan. Armenia has once against committed a provocation, ignoring law.”
He promised Turkey would stand by Azerbaijan and said, “Armenia is playing with fire and endangering regional peace.”
Turkish presidential spokesman Ibrahim Kalin also took to Twitter, condemning Armenia. “Armenia has violated the ceasefire by attacking civilian settlements … the international community must immediately say stop to this dangerous provocation.”
European Council President Charles Michel, meanwhile, tweeted that the news was a “serious concern.”
“Military action must stop, as a matter of urgency, to prevent a further escalation,” Michel said.