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About 200 U.S. troops will remain in Syria after the withdrawal of most U.S. military forces from the country, the White House said Thursday.

President Donald Trump declared in December that "we have won against ISIS" and that he would pull all of the 2,000 or so U.S. troops from the country, an announcement that surprised U.S. allies and senior military officials and plunged the U.S.-led campaign against ISIS into turmoil.

White House Press Secretary Sarah Sanders said Thursday that "a small peacekeeping group of about 200 will remain in Syria for a period of time," confirming a report last month by NBC News that some U.S. forces wouldn't be part of the withdrawal.

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NBC News quoted U.S. officials at the time as saying the United States hadn't figured out yet what level of support it would continue to provide in the fight against ISIS and that it was likely to maintain some sort of air presence in northern Syria.

The White House announcement came a day after The Washington Post quoted U.S. and foreign officials as saying the United States' European allies had rejected a request from the Trump administration to send their own troops to take up the slack from the U.S. withdrawal.

Sen. Lindsey Graham, R-S.C., a member of the Armed Services Committee, welcomed the White House announcement on Thursday.

"This will ensure ISIS does not return and Iran does not fill the vacuum that would have been left if we completely withdrew," Graham said. "This also ensures Turkey and SDF elements that helped us defeat ISIS will not go into conflict."

"SDF" is short for Syrian Democratic Forces, the U.S.-backed alliance of militias fighting to oust ISIS from the country.

"With this decision, President Trump has decided to follow sound military advice," Graham said. "This decision will ensure that we will not repeat the mistakes of Iraq in Syria. For a small fraction of the forces we have had in Syria, we can accomplish our national security objectives."