YEREVAN — 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.

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 demilitarized 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 Defense Ministry said two Azerbaijani helicopters were shot down and that Armenian forces hit three Azerbaijani tanks earlier in the day.

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.

Meanwhile, the Secretary General of the Gulf Cooperation Council Naif Al-Hajraf expressed his anxiety about the escalating tensions between the Armenia and Azerbaijan, due to their dispute over the Nagrono-Karabakh region.

In a statement issued on Sunday, Al-Hajraf stressed the importance of taking the dispute to the negotiating table, and halting these escalations within the framework of international law for the sake of the stability and security of the region and the world. — Euronews/SPA