At least 23 people were reported to have been killed on Sunday during a territorial dispute between Armenia and Azerbaijan.
Clashes took place between Armenia and Azerbaijan over the Nagorno-Karabakh region.
According to BBC, the region is identified as part of Azerbaijan. But it was controlled by Armenians.
Azerbaijani President Ilham Aliyev said on Sunday he was confident of regaining control over the region.
Authorities declared martial law in some areas of Azerbaijan, Armenia, and Nagorno-Karabakh.
The disputes in the Caucasus Mountains have remained unsolved for years.
At least 16 people were killed during border clashes in July, followed by the largest demonstration in years in the Azerbaijan capital Baku.
According to BBC, Any upsurge in violence could unsettle markets as the South Caucasus is a corridor for pipelines carrying oil and natural gas from the Caspian Sea to world markets.
World leaders reacted to the clash
Turkish President Recep Tayyip Erdogan has promised to support Azerbaijan. He has urged the world to stand with the country in its “battle against invasion and cruelty”.
On the contrary, seen as an ally of Armenia, has called for an immediate ceasefire and negotiations to control the situation. France has also urged Armenia to hold dialogues and impose a ceasefire.
Furthermore, UN Secretary-General Antonio Guterres said he was “extremely concerned” over and called for both sides to stop fighting
Iran, which borders both Azerbaijan and Armenia, offered to broker peace talks
President Donald Trump said the US was seeking to stop the violence