US President Donald Trump's decision to withdraw from Syria and allow a Turkish incursion into the north-east has caught many in the US government by surprise and sparked a storm of criticism on Monday from both parties in Congress.
The White House said that after a call with Mr Erdogan, Mr Trump decided that: "The United States Armed Forces will not support or be involved in the operation, and United States forces, having defeated the ISIS territorial 'caliphate', will no longer be in the immediate area.”
On Monday morning, a small contingent of US troops left two observation posts in Tal Abyad and Ein Eissa but it was unclear what the broader US plans were.
The US has about 2,000 troops in Syria. Its military announced in February that it would reduce this to 400 troops but Mr Trump is now again promising a full withdrawal.
He approved the Turkish operation into north-east Syria.
“Turkey will soon be moving forward with its long-planned operation into Northern Syria,” the White House said.
“The United States Government has pressed France, Germany, and other European nations, from which many captured ISIS fighters came, to take them back, but they did not want them and refused.
"The United States will not hold them for what could be many years and great cost to the United States taxpayer. Turkey will now be responsible for all ISIS."
But at the State Department and the Pentagon, US officials reached by The National were surprised by Mr Trump's decision.
One said that the officials were scrapping and reviewing their plans to adjust to Mr Trump’s pivot. He said that the US troops in north-west Syria were "in a state of limbo".
Nicholas Heras, a senior fellow at the Centre for New American Security, did not see a clear US plan.
“The US government is scrambling right now to make sense of Mr Trump's new policy,” Mr Heras said.
“There is no consensus on how this will all unfold, except that Turkey has neither the willingness nor the capability to prevent ISIS from re-emerging.”
Mr Heras said the decision could backfire and help ISIS.
“There is a morbid sense that this will result in the first stage of the ISIS recovery in Syria and that chaos will follow,” he said.
“With thousands of ISIS prisoners being held by the Syrian Democratic Forces, most of them local Syrians and Iraqis, there are all the ingredients for a massive ISIS jailbreak.”
The decision was also met by fierce criticism in Washington, including from Mr Trump’s Republican Party.
Senator Lindsey Graham, who has been called the president’s “whisperer”, said the decision was “a disaster in the making”.
He threatened Senate legislation to reverse the move, which he said was “a stain on America’s honour for abandoning the Kurds”.
A former member of Mr Trump’s cabinet who was ambassador to the UN, Nikki Haley, also criticised the decision.
“We must always have the backs of our allies if we expect them to have our back," Ms Haley tweeted under the hashtag “Turkey is not our friend”.
"The Kurds were instrumental in our successful fight against ISIS in Syria. Leaving them to die is a big mistake.”
Republican Congressman Adam Kinzinger said the withdrawal “would give Iran and Russia exactly what they want", while Republican Senator Marco Rubio called it a “grave mistake”.
Former US envoy in the fight against ISIS, Brett McGurk, who resigned last December, on Monday accused Mr Trump of lack of leadership.
“Donald Trump is not a Commander-in-Chief," Mr McGurk said. "He makes impulsive decisions with no knowledge or deliberation.
"The White House statement on Syria after Trump spoke with Erdogan demonstrates a complete lack of understanding of anything happening on the ground.”
Democrats also joined the chorus of criticism with former secretary of state Hillary Clinton and Senator Chris Murphy, among others, decrying the move.
But Mr Trump appeared to pull back some tacit support for a Turkish incursion into Syria later on Monday when he threatened to "obliterate" Turkish economy if it overstepped the mark.
"As I have stated strongly before, 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)," Mr Trump tweeted.
A US Defence spokesman said on Monday that the Pentagon "made clear to Turkey, as did the President, that we do not endorse a Turkish operation in northern Syria.
"The US Armed Forces will not support or be involved in any such operation."