Washington: President Donald Trump announced the complete, immediate withdrawal of US forces from Syria with a tweet and a video in December, overruling his generals, alarming Congress and allies and causing his defense secretary and another top aide to quit in protest.

But on Tuesday, he effectively reversed himself with a quick scrawl in black Sharpie - telling lawmakers he now agrees that some US forces should remain.

“I agree 100%,” Trump wrote in a handwritten notation on a letter sent by members of Congress expressing concern over his withdrawal plan. “All is being done.”

The missive marks a dramatic about-face from just 11 weeks ago, when Trump shocked allies and his own aides by abruptly declaring that “we have won” against Daesh and “now it’s time for our troops to come back home.” White House press secretary Sarah Sanders had previously announced that a small US force would remain in the war-torn country after all, but the letter amounts to Trump’s most definitive statement of his change of heart.

Trump penned his response - in bold lettering from the kind of marker he favours - directly on a copy of the letter from Sen. Lindsey Graham, R-S.C., and a bipartisan group of 11 other lawmakers who had written to the president on Feb. 22. The correspondence applauded the White House announcement on Feb. 21 that “a small peacekeeping group of about 200” US troops will stay in Syria beyond the planned withdrawal of most American forces this spring.

The White House announcement of a residual force apparently misstated the total - military officials have described plans for a force of about 400 - and did not specify its mission or duration.

Graham and other lawmakers had nonetheless welcomed it as a sign that Trump had listened to concerns that a complete withdrawal would endanger fragile military gains against Daesh.

“A stabilising force, which includes a small contingent of American troops and ground forces from our European allies, is essential to ensure stability and prevent the return of Daesh,” the senators wrote.