US President Donald Trump and Turkish leader Recep Tayyip Erdogan agreed in a phone conversation Sunday that they would work to prevent a power vacuum in Syria after American ground forces withdraw from the war-ravaged country.

Turkey applauded Trump’s widely criticized decision to pull his country’s 2,000 troops out of Syria, where they have been part of the multinational fight against ISIS.

“The two leaders agreed to ensure coordination between their countries’ military, diplomatic and other officials to avoid a power vacuum which could result following any abuse of the withdrawal and transition phase in Syria,” the Turkish presidency said in a statement.

Hours earlier Trump had tweeted that he and Erdogan “discussed ISIS, our mutual involvement in Syria, & the slow & highly coordinated pullout of U.S. troops from the area.”

Erdogan tweeted shortly thereafter, saying the two leaders “agreed to increase coordination on many issues including trade relations and the developments in Syria,” dubbing the call “productive.”

US troops will leave under the auspices of a new Pentagon chief set to start next month, after Jim Mattis resigned from the post citing key differences, including on Syria, with the frequently impulsive president.

A US withdrawal would allow Turkish troops to move against Kurdish fighters in Syria who have played a key role in the war against ISIS but are deemed terrorists by Ankara.

Many US politicians and international allies fear the withdrawal is premature and would further destabilize the already devastated region.

A US withdrawal, said Mutlu Civiroglu, a Kurdish affairs analyst, will open the way “for Turkey to start its operations against the Kurds, and a bloody war will begin.”

French President Emmanuel Macron on Sunday said he “deeply regretted” Trump’s decision, and that “an ally must be reliable.”

Several US politicians from both parties rejected Trump’s claim that ISIS had been defeated, and many in the US military expressed alarm and dismay at the thought of suddenly abandoning Washington’s Kurdish partners.

And Trump’s sudden decision, which he announced on December 19, sparked further turmoil within his troubled administration, prompting the resignation of Mattis as well as of Brett McGurk, the special envoy to the anti-ISIS coalition.

– with reporting by Agence France-Presse