New Delhi: At least 23 people including civilians and combatants were killed and over 100 sustained injuries on Sunday (local time) as two Asian countries Azerbaijan and Armenia entered a fight.  Heavy clashes broke out between Armenian and Azerbaijani forces over the disputed separatist region of Nagorno-Karabakh.

Sixteen Armenian separatist fighters were killed and more than 100 wounded in the fighting, rebel officials said, Al Jazeera reported. Both sides also reported casualties including at least one Armenian woman and child. An Azerbaijani family of five was reportedly killed in shelling launched by Armenian separatists.

As per a  report in BBC, Armenia also accused Azerbaijan of air and artillery attacks and reported downing helicopters and destroying tanks, and declared martial law, while Azerbaijan said it had begun a counter-offensive in response to shelling.

On Sunday, a heavy fighting between the forces of Azerbaijan and Armenia broke out in the disputed region of Nagorno-Karabakh region, while both countries blamed each other for the escalation that led to casualties.

What is the conflict about:

The regions have had a history of unresolved dispute. The conflict in the Caucasus Mountains has remained unresolved for more than three decades, with periodic bouts of fighting. The conflict in the Nagorno-Karabakh region was sparked following the breakdown of the Soviet Union, which continued from late 1980s to around 1994, with both the countries claiming the territory.  A ceasefire signed after this provided for two decades of relative stability, which however deteriorated along with Azerbaijan's increasing frustration with the status quo, at odds with Armenia's efforts to cement it.

Border clashes in July which were the worst among the many bouts of clashes, killed at least 16 people, prompting the largest demonstration for years in the Azerbaijani capital Baku, where there were calls for the region's recapture.

UN calls for de-escalation

United Nations Secretary-General Antonio Guterres “calls on the sides to immediately stop fighting, de-escalate tensions and return to meaningful negotiations without delay,” said his spokesman Stephane Dujarric.

US Deputy Secretary of State Stephen Biegun  also called the foreign ministers of Armenia and Azerbaijan to urge cessation of hostilities, said State Department spokesperson Morgan Ortagus.