US President Donald Trump on Monday threatened to “totally destroy and obliterate” Turkey’s economy if it took any action he considered “off-limits” following his decision to withdraw American forces from northeastern Syria.

The withdrawal, announced by the White House late on Sunday, was swiftly condemned by a bipartisan group of lawmakers over concerns that it could open the way for a Turkish strike on Kurdish-led forces long allied with Washington.

“As I have stated strongly before, and just to reiterate, if Turkey does anything that I, in my great and unmatched wisdom, consider to be off limits, I will totally destroy and obliterate the Economy of Turkey (I’ve done before!)” Trump tweeted.

The United States began pulling troops back from the northeast Syrian border on Monday. The major policy shift was denounced as a “stab in the back” by Kurdish-led forces who have been Washington’s most capable partners in fighting Islamic State in Syria.

The Kurdish forces, known as the Syrian Democratic Forces (SDF), accused Washington of reneging on an ally, warning it would have a “great negative” impact on the war against the militants.

The White House statement on Sunday appeared to hand Turkey responsibility for Islamic State captives who are held in SDF facilities south of Turkey’s initially proposed safe zone.The United States does not endorse Turkey’s planned offensive in northern Syria and the U.S. military will not support it in any way, the Pentagon said on Monday, moving to distance itself from an operation that threatens U.S.-backed Syrian Kurdish fighters.

“The Department of Defense made clear to Turkey - as did the President - that we do not endorse a Turkish operation in Northern Syria. The U.S. Armed Forces will not support, or be involved in any such operation,” Pentagon spokesman Jonathan Hoffman said in a statement.

U.S. Defense Secretary Mark Esper and Chairman of the Joint Chiefs of Staff Army General Mark Milley have told “their respective Turkish counterparts that unilateral action creates risks for Turkey,” Hoffman said.

Meanwhile, France will monitor closely a U.S. withdrawal from northern Syria and a possible Turkish offensive because it could strengthen Islamic State, its armed forces minister said on Monday.

“We have to be extremely vigilant that such a move, which goes against the objectives of the (anti-Islamic State) coalition, could strengthen Islamic State rather than weakening or destroying it,” Florence Parly told reporters in northern France.