Armenia has accused Turkey of backing the Azerbaijani side in the battle for the Nagorno-Karabakh region and has called on NATO to rein in its ally.

But Stoltenberg, who met Armenia's President Armen Sarkisian at NATO's Brussels headquarters on Wednesday, said both Armenia and Azerbaijan were valued partners of the alliance and refused to take sides in the fighting.

On Thursday, however, at a news conference after a meeting of defence ministers, he did suggest that Turkey must be part of a diplomatic solution to the conflict, and deplored reports of civilian deaths.

"We need an immediate ceasefire and full respect for the ceasefire and cessation of all her hostilities and therefore call on both Armenia and Azerbaijan, to cease fighting," he told reporters.

"That was the message yesterday, that is the message today, and that has been my current message over the last weeks.

"... Turkey is a valued ally, but I also expect Turkey to use its considerable influence in the region to calm tensions."

Hundreds of people -- both civilians and combatants -- have already been killed in the latest flare-up of fighting over Karabakh, a region of Azerbaijan long controlled by Armenian separatists, and Armenia's Prime Minister Nikol Pashinyan has warned there will be no diplomatic solution "for a long time".