ANKARA: The head of NATO said Monday he expected Turkey - a key ally of Azerbaijan - to use its "considerable" influence to calm the conflict in the Armenian separatist region of Nagorno-Karabakh.

Secretary General Jens Stoltenberg's comments in Ankara came as fighting between Azerbaijani and Armenian separatist forces entered its second week with at least 260 people killed.

"We are deeply concerned by the escalation of hostilities. All sides should immediately cease fighting and find a way forward towards a peaceful resolution," Stoltenberg said after talks with Turkish Foreign Minister Mevlut Cavusoglu.

"And I expect Turkey to use its considerable influence to calm tensions."

Turkish President Recep Tayyip Erdogan has urged fellow Muslim Azerbaijan to press on with its campaign until it takes back lands it lost in an early 1990s war that claimed 30,000 lives as the Soviet Union fell apart.

Cavusoglu said NATO should approach the escalation "in a balanced fashion".

"Everyone, particularly NATO, should call on Armenia to withdraw," Cavusoglu said.

Stoltenberg's visit to Turkey came during a new spell of tensions with its strategically vital member states.

Turkey contributes one of the largest forces to the Western military alliance and plays a crucial role in Libya and the Middle East.

But Turkey's hunt for natural gas in disputed waters in the eastern Mediterranean has resulted in staging rival war games with fellow NATO member Greece.