WASHINGTON, Dec 19 : The Trump administration will withdraw all of the approximately 2,000 American troops in Syria, according to a U.S. official, as the White House declared victory Wednesday in the mission to defeat Islamic State militants there.

Planning for the pullout has begun and troops will begin leaving as soon as possible, said the official, who was not authorized to publicly discuss military planning and spoke on condition of anonymity. President Donald Trump said American forces no longer were needed in a country torn apart by long-running civil war.

Trump has said since he was a presidential candidate that he wanted to bring back troops from the Middle East. But officials have said in recent weeks that pockets of IS militants remain. U.S. policy has been that American forces would stay in place until the extremists were eradicated.

In addition, Pentagon and other officials have said that U.S. troops were countering Iran-backed militants in Syria, which was an expansion of the U.S. mission.

Trump said on Twitter: “We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency.”

His tweet followed a series of news reports that the U.S. was preparing to withdraw its troops from Syria. The news was first reported by The Wall Street Journal.

Reports of an abrupt withdrawal drew quick criticism from Congress. Sen. Marco Rubio, R-Fla., said a full and rapid removal of troops would be a “grave error with broader implications” beyond the fight against IS.

Responding to the reports, Pentagon spokesman Col. Rob Manning said in a statement that “at this time, we continue to work by, with and through our partners in the region.”

The U.S. first launched airstrikes against IS fighters in Syria in 2014. In the years that followed, the U.S. began partnering with Syrian ground forces to fight the extremists.

The Pentagon recently said that IS now controls just 1 percent of the territory they originally held.