WASHINGTON :- President Donald Trumpinfo-icon has begun what will be a total withdPresident Donald Trump has begun what will be a total withdrawal of United Statesinfo-icon troops from Syriainfo-icon, declaringrawal of United States troops from Syria, declaring on Wednesday (Dec 19) that they have succeeded in their mission to defeat the Islamic Stateinfo-icon in Iraqinfo-icon and Syria (ISIS) and were no longer needed in the country.

Mr Trump said on Wednesday that it was time for USinfo-icon troops to come home from Syria, after years of battling the ISIS militant group in the warinfo-icon-wracked country.  

"We won," Mr Trump said in a video message posted on Twitterinfo-icon, declaring the ISIS militants defeated. "We've beaten them and we've beaten them badly. We've taken back the land... So our boys, our young women, our men - they're all coming back and they're coming back now."

His message came at the end of a day of relative surprise in Washington at the news that the 2,000 US troops on the ground in Syria would be withdrawn.

A US official said Mr Trump's decision was finalised on Tuesday. 

In his video message, the Republican President - facing criticism on both sides of the political aisle - insisted the time was right.  "They're getting ready. You're going to see them soon. These are great American heroes," Mr Trump said. 

But the move could leave the US with few options to prevent a resurgence of ISIS. It could also undercut US leverage in the region and undermine diplomatic efforts to end the Syrian civil war, which is now in its eighth year.

News of a full withdrawal drew immediate criticism from some of Mr Trump's fellow Republicans, who said that leaving strengthened the hand of Russiainfo-icon and Iraninfo-icon, which both support Syrian President Bashar al Assad.

It may also leave exposed an alliance of Kurdish and Arab militias known as the Syrian Democratic Forces, or SDF, which has been among the most effective against ISIS but is under threat, as Turkeyinfo-icon weighs a new offensive in Syria.

US commanders on the ground, who have developed strong ties to SDF leaders, had voiced concerns about what a fast withdrawal would mean for the US-backed forces and were surprised by the decision, US officials told Reuters, speaking on condition of anonymity.

"We have started returning United States troops home as we transition to the next phase of this campaign," White House spokesman Sarah Sanders said in a statement issued after Mr Trump tweeted: "We have defeated ISIS in Syria, my only reason for being there." 

Mr Trump's predecessor, Mr Barack Obama, was slow to get involved in Syria's civil war, fearing being dragged into another open-ended foreign conflictinfo-icon like the one in Afghanistaninfo-icon. Hundreds of thousands of people have been killed in Syria and around half its pre-war 22 million population displaced.

But in a campaign to defeat ISIS in Syria, Mr Obama ordered air strikes from September 2014 and then troops into the country the following year.

One US official said Washington aimed to withdraw troops within 60 to 100 days and said the US State Department was evacuating all its personnel in Syria within 24 hours. A second official said they could leave even sooner.

TRUMP'S WARINESS 

Mr Trump is wary of open-ended foreign conflicts and his decision on Syria raises questions about whether he may also reconsider the US war effort in Afghanistan, where American forces have been fighting since 2001.

Mr Trump reluctantly agreed to a troop increase last year but US officials have privately acknowledged a sense of urgency and are increasingly focused on securing a peace deal with a resurgent Taleban.

Some of Mr Trump's Republican allies in Congress railed against the pullout decision. US Senator Lindsey Graham, often a Trump ally but generally a foreign policyinfo-icon hawk, said a withdrawal would have "devastating consequences" for the US in the region and throughout the worldinfo-icon.

"An American withdrawal at this time would be a big win for ISIS, Iran, Bashar al Assad of Syria, and Russia," Mr Graham said in a statement.

The surprise decision also raised eyebrows abroad.

A British defence minister said he strongly disagreed with Mr Trump that ISIS had been defeated in Syria. Israeli Prime Minister Benjamin Netanyahu said Israelinfo-icon would study the decision and would ensure its own security.

In Russia, TASS news agency quoted the Foreign Ministry as saying withdrawing US troops from Syria created prospects for a political settlement.