Trump's call to leave Syria slammed by Republicans

US President Donald Trump's latest call to end American involvement in Syria was slammed by Republicans, who warned that abandoning a key ally, the Kurds, and walking away from the fight against the IS would cause irreparable damage to Washington's interests.

Congressional leaders including Republican Senators Marco Rubio of Florida, Ted Cruz of Texas along with top Democrats sharply criticized Trump's decision, reports Efe news.

Senate Majority Leader Mitch McConnell, a Kentucky Republican, urged Trump to "exercise American leadership" and keep US troops in northern Syria.

"American interests are best served by American leadership, not by retreat or withdrawal," McConnell said on Monday.

He didn't directly criticize Trump, but reminded him of the Senate's January vote to keep US troops in Syria.

In the wake of the criticism, Trump tweeted on Monday that he would "totally destroy and obliterate the economy of Turkey" if Ankara did anything off limits.

Hours earlier, he had said the US would stand aside to let Turkey launch a military offensive against Kurdish fighters in northeastern Syria.

The President's latest shift on Syria comes against a backdrop of increased pressure from the Democratic-led House which has launched an impeachment inquiry against Trump in connection with his request that Ukraine investigate his political rival and former Vice President Joe Biden.

Last year, Trump abruptly ordered a full withdrawal of US forces, triggering the resignation of then Defence Secretary Jim Mattis. Amid an outcry, Trump reversed course and decided to keep some US forces in Syria to prevent a resurgence of the Islamic State (IS) terror group and to challenge Iranian and Russian influence.

Dozens of US special-operations forces began moving away from the border between Syria and Turkey on Monday, repositioning within the country, but not withdrawing for now, US defence officials said.

There were no further US troop movements, and US officials have downplayed prospects for any wholesale withdrawal of the roughly 1,000 troops from Syria.

A senior administration official said that the US had no plans to leave Syria and moved about 100 troops to other parts of the country as a precautionary measure.

"We don't want those (US) troops to be there and thus send a signal that they are supporting the (Turkish) operation, nor do we want them to be there and look like we may be trying to stop the Turks from moving in," the official said. "So therefore the best thing is just to get some troops out of the way."

Meanwhile, the US-backed Syrian Democratic Forces, a Kurdish-led group, said it had been betrayed by Washington and vowed to fight "at all costs".

"We in the SDF will not hesitate for a moment to defend ourselves and we call on our people of all sects and ethnicities... to close ranks with their legitimate forces to defend our country against this Turkish aggression," the group said.

Trump signaled during a White House appearance on Monday afternoon that he still wanted an eventual US withdrawal.

"Once we captured IS, I don't want to stay there for the next 40 years," Trump said. "It's not going to do anything."

"We want to bring our troops back home, and I got elected on that."

Kurdish leaders in Syria long feared that the US would abandon them after the fight against IS, despite assurances from top American officials.