Updated at 4:34 p.m. ET
The Trump administration is changing the number of American troops that will remain in Syria.
Approximately 400 troops will stay there, a senior administration official has told NPR. That's double the number announced Thursday night by White House press secretary Sarah Sanders.
In Thursday's one-sentence statement, Sanders said: "A small peacekeeping group of about 200 will remain in Syria for a period of time." But the senior administration official said Friday the troops will be "observers and monitors," and not a U.N.-style peacekeeping force.
The official said there is no timeline for the mission and no date for withdrawal.
About 200 troops will remain in the Syrian town of al-Tanf, near the border with Iraq. Their mission is to counter Iran and support U.S. forces in Iraq.
Another 200 will remain in northern Syria and be part of a "multinational observer force" numbering between 800 and 1,500, mostly European NATO allies, including France and Britain. They are located in the "safe zone" on the Turkish-Syrian border controlled by Kurdish allies of the U.S. who have led the ground war against ISIS. The American troops will be combat-ready but their role is to monitor the region.
According to The New York Times, the Sanders announcement came after a phone call between President Trump and Turkey's President Recep Tayyip Erdogan, in which the two leaders agreed to create a safe zone in Syria.
In December, the White House said it would pull all 2,000 troops from Syria, a reversal of U.S. policy that reportedly was met with disapproval within the Pentagon and prompted Defense Secretary Jim Mattis to resign in protest. Troops began withdrawing in January, sparking criticism that the U.S. was leaving before it had completely eradicated the Islamic State presence there.
At a security conference in Munich last week, the U.S. encouraged its European allies to remain in Syria even as it was withdrawing. German Chancellor Angela Merkel criticized the U.S. plan. "Is it a good thing to immediately remove American troops from Syria, or will it not strengthen Russia and Iran's hand?" she said.
Some have worried that Russia and Iran would fill the vacuum created by a U.S. pullout.
A senior administration official told the Times that the decision to leave some troops in Syria was intended to encourage France and Britain to also keep troops there. European countries had "unanimously" told the U.S. they wouldn't stay if American forces left, The Washington Post reported, quoting a senior administration official.
Sen. Lindsey Graham, chairman of the Senate Judiciary Committee, applauded the decision. "This will ensure ISIS does not return and Iran does not fill the vacuum that would have been left if we completely withdrew," he said in a statement.
Graham, who had been critical of Trump's December decision to pull all troops, said keeping forces there ensures that the U.S. won't repeat the mistakes it made in Iraq. "This also ensures Turkey and [Syrian Democratic Forces] elements that helped us defeat ISIS will not go into conflict," he said.