Pentagon defends Syria withdrawal as 'deliberate, well thought-out, mutually supportive, and controlled' in a tweet

The Defense Department is defending President Trump's decision to pull 2,000 U.S. troops out of Syria, tweeting on Friday that the withdrawal is "deliberate, well thought-out, mutually supportive, and controlled."

The department also called the withdrawal the "next phase" of U.S. support to the U.S.-led coalition's operations in Syria, but did not provide further detail about what that support looks like.

The tweet was a markedly firm defense of the president's announcement last week that he would pull all U.S. troops out, shocking top U.S. officials, allies, and partners. The decision to withdraw ran counter to State Department and Defense Department messaging on U.S. policy in Syria, and led to the resignation of Secretary of Defense James Mattis and the top U.S. envoy in the fight against ISIS.

The tweet did not specify which parties were "mutually supportive" of the decision to withdraw U.S. troops, but critics of the decision have raised concerns about the abandonment of the U.S.-backed Kurdish forces who were integral to the coalition's fight against ISIS but who Turkey considers to be an element of an insurgent group.

Since the U.S. announcement last week, the Kurds have asked the Syrian army to control the northern Syrian city of Manbij, seeking protection from a possible Turkish invasion.

Trump's decision to withdraw U.S. troops originated from a phone call with Turkish President Recep Tayyip Erdogan on Dec. 14 in which Erdogan reportedly promised to finish off the fight against ISIS in Syria if the U.S. pulled out its forces.

Five days later, as news of the impending withdrawal broke, the president declared on Twitter that ISIS had been defeated, surprising top officials, many of whom had only learned of the change in policy the day before.

Outgoing Defense Secretary Mattis was among several of the president's top advisers who urged him not to make a hasty withdrawal. He resigned the next day, writing that the president should have a defense secretary whose views were "better aligned" with his own.

State Department and Pentagon officials had cautioned as recently as the week before the decision was publicized that the fight against ISIS was not over -- with the coalition recently estimating that about 2,000 ISIS fighters remain in Syria.

In the immediate aftermath of the announcement, U.S. officials had said it was likely that the U.S. troops in Syria could all be pulled out in 30 days. But officials told ABC News this week that as plans have been developed, the pace of withdrawal could be much slower -- with troops leaving over the course of several months. However, no final decision has been made, officials said.