Turkey came in for some harsh criticism for its invasion of northeast Syria during a two-day October 24-25 meeting of Nato defence ministers in Brussels, with concerns over Ankara’s growing cooperation with Moscow also expressed.

US Defense Secretary Mark Esper called the incursion, which started on October 9, "unwarranted". "Turkey put us all in a very terrible situation," Esper said.

Adding that Turkey is heading in the “wrong direction” he noted: “We see them spinning closer into Russia's orbit than into the Western orbit. And I think that's unfortunate.”

Nato secretary-general Jens Stoltenberg said the military alliance has "seen disagreements before" between its members, but said it has always endured.

Closer relations between Turkey and Russia over Syria could tilt the balance of international power and push Europe to re-evaluate its geopolitical strategy, Bloomberg reported on October 24, citing an unnamed French diplomat.

Turkish President Recep Tayyip Erdogan and Russian counterpart Vladimir Putin on October 22 announced a deal to establish a buffer zone in northern Syria where Turkish and Russian forces will conduct joint patrols 10-km deep along Turkey’s southern border. Ankara says the zone is necessary to keep the border area free of “terrorist” and “insurgent” Kurdish fighters.

The row over Ankara’s move into northeastern Syria caused such tensions in Nato that Spain threatened to withdraw its Patriot missiles from Turkey in protest. Nato member countries criticised Turkey for jeopardising the fight against Islamic State militants in Syria by attacking and displacing the Kurds who were supposed to be keeping the militants under lock and key.

But the Nato allies know full well that Turkey is crucial to their alliance, given its strategic position between Europe and Asia. Efforts will be made to ensure Turkey is not driven to considering leaving the military bloc.

"There's a concerted effort not to make things worse," one Nato diplomat told Reuters during the meeting of defence ministers, including Turkey's Hulusi Akar. "Turkey, after [US President Donald] Trump, has put a renewed strain on the alliance. But Turkey is too important to lose."