US going into Middle East ‘worst decision ever’: Trump

US President Donald Trump said the US military becoming involved in the Middle East was the "worst decision ever made" and that he was ensuring the safe return of troops.

Trump has faced a bipartisan storm of criticism since a surprise announcement by the White House on Sunday that Washington was pulling back 50 to 100 "special operators" from Syria's northern frontier.

"GOING INTO THE MIDDLE EAST IS THE WORST DECISION EVER MADE IN THE HISTORY OF OUR COUNTRY! We went to war under a false & now disproven premise, WEAPONS OF MASS DESTRUCTION. There were NONE!" the president tweeted in reference to the 2003 US invasion of Iraq.

The United States is estimated to have between 60,000 and 80,000 troops across the area covered by US Central Command, which includes Afghanistan, Iraq and Syria.

Trump bemoaned what he called the "eight trillion-dollar" bill for "fighting and policing" in the Middle East, and the thousands of US soldiers who had been killed or wounded in battle.

"Now we are slowly & carefully bringing our great soldiers & military home. Our focus is on the BIG PICTURE! THE USA IS GREATER THAN EVER BEFORE!" Trump said.

Republicans savaged Trump Wednesday for allowing Turkey to attack US allies in Syria as the president offered varying reasons for giving Turkey the green light, including the fact that Kurds did not fight alongside the US in World War II.