US President Donald Trump has threatened to “devastate Turkey economically” if it attacks US backed Kurdish militants in Syria after US withdrawal.

"Starting the long overdue pullout from Syria while hitting the little remaining ISIS territorial caliphate hard, and from many directions. Will attack again from existing nearby base if it reforms," the president said on Twitter Sunday.

He further warned that he "will devastate Turkey economically if they hit Kurds," adding in a second tweet, "Likewise, do not want the Kurds to provoke Turkey."

The US president also overstated the Washington’s alleged role in fighting the ISIL Takfiri terrorists in Syria.

"Russia, Iran and Syria have been the biggest beneficiaries of the long term U.S. policy of destroying ISIS in Syria - natural enemies. We also benefit but it is now time to bring our troops back home. Stop the ENDLESS WARS!" Trump said.

Turkish President Recep Tayyip Erdoğan publicly lashed out at US national security adviser John Bolton last week.

US presence in Syria has had no approval from the Syrian government or a mandate from the United Nations.

Trump announced via Twitter on December 19 that all American troops in Syria would be withdrawn from the Arab country.

He initially indicated that the withdrawal would be quick but has since stated that it would be "slow and coordinated" with allies.

Russia and Iran have been both assisting Syria in its counter-terrorism offensive and mediating, together with Turkey, a diplomatic process to help restore calm to the Arab country.