Trump orders full withdrawal of US troops from Syria

President Donald Trump has announced the withdrawal of all 2,000 US troops from Syria as he abruptly declared victory over ISIL in the country in a move that contradicted his own experts' assessments and sparked surprise and anger among senior fellow Republicans who railed against it.

"We have defeated ISIS in Syria, my only reason for being there during the Trump presidency," Trump said on Wednesday, referring to the armed group that once controlled vast areas of Syria and Iraq but is now confined to small pockets.

US officials said many details of the troop withdrawal had not yet been finalised, but they expect their country's forces to be out by mid-January.

Washington began air raids in Syria in 2014, a year before US ground troops moved in to fight the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) armed group and train Syrian rebels in the war-ravaged country.

Later on Wednesday, Trump suddenly declared their mission accomplished, posting a video on Twitter in which he said is "heartbreaking" to have to write letters and make calls to the loved ones of those killed in battle.

"Now it's time for our troops to come back home," said Trump, who has long stated a desire to bring soldiers based in Syria back to the United States.

Trump's decision immediately triggered demands from Congress, including senior Republicans, for more information and a formal briefing on the matter.

A senior administration official, speaking to reporters on condition of anonymity, said Trump made the unilateral decision based on his belief that US troops have no role in Syria beyond combatting ISIL.

The US president informed his Turkish counterpart, Recep Tayyip Erdogan, of his move in a telephone call, the official said, adding that Trump "made his own decision" and did not discuss the matter with Turkey's leader.

Turkey, a NATO ally, has recently warned that it will launch combat operations across its southern border into northeastern Syria against an alliance of Kurdish and Arab groups known as the Syrian Democratic Forces, or SDF, who have been allied with the US in the battle against the ISIL.

The partnership with the SDF has outraged Ankara, which views the US-backed Kurdish People's Protection Units (YPG) as an extension of an armed group fighting inside Turkey.

In recent days, Turkey again voiced frustration about what it says are delays in the implementation of a deal with the US to clear the YPG from the town of Manbij, located west of the Euphrates in YPG-controlled areas.

Britain, meanwhile, said it strongly disagreed with Trump that ISIL had been defeated in Syria, while Israeli Prime Minister Benjamin Netanyahu said Israel would study the decision and would ensure its own security.

In Russia,  a major ally of Syrian President Bashar al-Assad, along with Iran, TASS news agency quoted the foreign ministry as saying that withdrawing US troops from Syria created prospects for a political settlement.

Trump's declaration of victory was far from unanimous and officials said US defence and military leaders were trying to dissuade him from ordering the withdrawal right up until the last minute.

News of a full withdrawal drew immediate criticism from some of Trump's fellow Republicans, who said that leaving strengthened the hand of al-Assad allies, Russia and Iran.

Senator Lindsay Graham, typically a Trump backer, called the decision "a disaster in the making". He added: "The biggest winners in this are ISIS and Iran."

Marco Rubio, another Republican senator, called the move a "grave error" adding that Kurdish fighters will stop fighting ISIL when they had to confront Turkish troops crossing the border into Syria. "This is a bad idea because it goes against the fight against ISIS and potentially helps ISIS," he said, warning it could trigger a broader conflict in the region.

"Now that the US has withdrawn or is going to withdraw from Syria, we have basically turned the country over to Russia and, to an even greater extent, Iran."  

But fellow Republican Senator Rand Paul backed Trump's decision.

"For the first time in my lifetime, we have a president with the courage to declare victory and bring our troops home," he told reporters.