Fighting between Armenia and Azerbaijan broke out on Sunday around the separatist region of Nagorno-Karabakh with reports of two Azerbaijani helicopters being shot down.
The Armenian Defence Ministry said its forces hit three Azerbaijani tanks and destroyed two helicopters. They also report 16 of their soldiers and two civilians have been killed and more than 100 others wounded.
Azerbaijan's president reported civilian casualties and both sides blamed each other for starting the attack.
Nagorno-Karabakh is an ethnic Armenian enclave within Azerbaijan that has been out of Azerbaijan’s control since the end of a war in 1994.
Both sides have heavy a military presence along a demilitarised zone separating the region from the rest of Azerbaijan.
Azerbaijan’s defence ministry denied the claim that its helicopters and tanks had been hit.
President Ilham Aliyev said in a televised address to the nation that “there are losses among the Azerbaijani forces and the civilian population as a result of the Armenian bombardment".
The news was harshly received in Turkey, a close ally of Azerbaijan.
Turkey’s ruling party spokesperson 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 spokesperson Ibrahim Kalin also took to Twitter to condemn Armenia, writing: “Armenia has violated the ceasefire by attacking civilian settlements... the international community must immediately say stop to this dangerous provocation.”
Turkey and Armenia have a difficult relationship due to the legacy of the Armenian Genocide carried out by the Ottoman Turks.
Mostly mountainous Nagorno-Karabakh — a region some 1,700 square miles lies 30 miles (50km) from the Armenian border.
Local soldiers backed by Armenia also occupy some Azerbaijani territory outside the region.
International efforts to settle the conflict have stalled and fighting sporadically breaks out.
In July, one of the most severe outbreaks of fighting in years left 16 people from both sides dead.