US President Donald Trump had ordered the withdrawal in December after he said they had defeated Islamic State militants in Syria, according to Reuters.

But he was persuaded by advisers on Thursday that about 200 US troops would join what is expected to be a total commitment of about 800-1,500 troops from European allies to set up and observe a safe zone being negotiated for northeastern Syria, the official told reporters.

About 200 other US troops will remain at the US military base at Tanf, near the border with Iraq and Jordan.

“We don’t want to see a resurgence of IS,” the official said.

Marine General Joseph Dunford, chairman of the Joint Chiefs of Staff, has been in talks with European counterparts about the safe zone in northeastern Syria.

But on Monday, US officials concluded that Europeans would not be willing to go it alone without some US participation, the official said.

The combat-ready US and European forces will help keep the peace between Kurdish forces, who supported the fight against Islamic State, and Turkey, the official said.

“Yesterday I asked the president for a couple hundred - he said yes,” said the official, who spoke on condition of anonymity.

“It’s not a firm number, and the president understood that when we asked him,” the official said.

Trump made the decision just before speaking to Turkish President Tayyip Erdogan by phone on Thursday, and suggested to Erdogan that Turkish military officials continue the discussions while visiting their counterparts in Washington on Friday.

There were no firm commitments on troops for the safe zone from European allies as of Friday, and those talks continue.

“I’m very optimistic about it, but it’s not done yet,” the official said.

Separately, Marine General Joseph Dunford, chairman of the Joint Chiefs of Staff, said: “There is no change in the basic campaign [in Syria]. The resourcing is being adjusted because the threat has been changed.”

He added that he was confident that US allies would step up in Syria.

Reporter’s code: 50101