Turkish deaths in Syria prompt Nato alarm

"This dangerous situation must be deescalated," he said.

"We have seen bombing of civilian targets. We have seen increased humanitarian suffering and hundreds of thousands of people have been forced to leave their homes," Stoltenberg added, referring to Russia and Syria's joint assault on rebels in the Idlib region in northwest Syria.

Turkey called the Nato meeting after 33 of its soldiers were killed in Idlib on Thursday.

It invoked Article Four of the Nato treaty, saying its "territorial integrity, political independence, or security" had been "threatened".

It blamed air strikes by the Syrian regime of president Bashar al-Assad for the deaths and threatened massive reprisals.

But Assad's ally, Russia, said Syrian artillery killed the Turkish soldiers by accident.

Russia also accused Turkish forces of secretly fighting alongside Syrian rebels against Assad. And it sent two high-end warships to the area in a show of strength.

The Syria conflict began nine years ago in spring 2011 as a civilian uprising.

But it later turned into a more complex theatre, involving Islamist radicals, Kurdish separatists, and Middle East and geopolitical rivals.

For their part, Russia and Turkey have strong relations outside Syria.

These were already once tested when Turkey shot down a Russian plane on the Turkish-Syrian border in 2015.

But Russian president Vladimir Putin spoke softly of the latest incident in Idlib with Turkish president Recep Tayyip Erdogan in a phone call on Friday.

"They voiced their concern about the escalation of tension in Idlib, which resulted in numerous casualties, including among Turkish military personnel," a Kremlin statement said.

They agreed to step up defence coordination to avoid accidental clashes.

And they "stressed that the priority task was to fight international terrorist groups" in Syria.

At the same time, Turkey has harmed ties with its Western friends due to Erdogan's authoritarian crackdown at home and his hawkish foreign policy.

But Nato's Stoltenberg also voiced "deepest condolences for the death of Turkish soldiers" on Friday.

Nato would build up Turkey's air defences and was helping it with Awacs air-surveillance planes, he added.

"The meeting we had today is a clear demonstration of Nato solidarity and expression of support from all the Nato allies," he said.