WASHINGTON, Dec. 19 (Xinhua) -- The Trump administration announced Wednesday that it has started returning U.S. troops home from Syria after claiming a victory in the fight against the Islamic State (IS), declining to provide more details on the exit timetable.

The move drew mixed reactions at home and abroad, complicating the Syrian situation and leaving U.S. military presence in Iraq and Afghanistan in doubt.

SURPRISE, NO SURPRISE

"We have started returning United States troops home as we transition to the next phase of this campaign," said White House Spokesperson Sarah Sanders in a statement on Wednesday morning, claiming that America has "defeated the territorial caliphate."

The White House announcement caught many people off guard.

"It's a surprise to me," Brookings Institution senior fellow Michael O'Hanlon told Xinhua.

"I've never seen a decision like this since I've been here, 12 years, where nothing is communicated in advance. And all of a sudden this type of massive decision takes place," Bob Corker, chairman of the Senate Foreign Relations Committee, told U.S. media. "It's caught everybody off guard."

But the decision did not come out of nowhere as U.S. President Donald Trump "always doubted the Syria mission even more," O'Hanlon noted.

Over the past months, Trump has reiterated his intention of bringing American troops back from Syria, claiming that the costly U.S. military presence in the Middle East has brought "nothing, except death and destruction."

However, the Pentagon and U.S. State Department officials have voiced concern on different occasions that a much longer-term effort was necessary to fully defeat the militant group of the IS.

Brett McGurk, the U.S. envoy to the coalition fighting IS, said in a speech last week that "even as the end of the physical caliphate is clearly now coming into sight, the end of ISIS (IS) will be a much more long-term initiative."

"Nobody is declaring a mission accomplished," McGurk said.

MIXED RESPONSES

Trump's decision to pull U.S. forces out of Syria has been questioned as well as hailed at home and abroad.

Senior Republican Senator Lindsey Graham warned of "devastating consequences" for U.S. troops quitting Syria.

"An American withdrawal at this time would be a big win for ISIS, Iran, Bashar al Assad of Syria, and Russia," the lawmaker from the state of South Carolina said in a statement on Wednesday.

"Both the Trump and Obama Administrations in Syria went far beyond the congressionally authorized use of force to go after terrorists... I am pleased (Trump) is bringing our troops home," said Democratic Congressman Ted Lieu in a tweet.

Russian Foreign Ministry Spokesman Maria Zakharova said on Wednesday that the U.S. decision creates good prospects for a political solution in that Arab country.

"I strongly disagree. It has morphed into other forms of extremism and the threat is very much alive," tweeted British Defense Minister Tobias Ellwood, following Trump claiming U.S. victory over IS on Twitter.

POWER PLAY CONTINUES

After the announcement from the White House, whether there will be a full U.S. withdrawal from Syria has been questioned.

Brookings Institution senior fellow Darrell West said he believes that special forces and air power likely will remain there to safeguard American interests.

"Trump wants the public to see the Syria campaign as an American victory over ISIS. That will allow him to claim credit for a military gain," West told Xinhua. "But he (Trump) can't go too far with a withdrawal without providing a major opportunity for other countries to fill the void."

The U.S. decision came as Turkey is planning to renew a military campaign against the Kurdish militia in eastern Euphrates, which has been relying on Washington in its operations against militants in the last IS-held pocket in the area.

Kurdish leaders said on Wednesday if the United States pulled out from the region, it would be a stab in the back for the Kurdish groups, according to a report from a London-based watchdog.

"If the U.S. trip wire is removed, the Turks, Syrian regime forces, their Iranian allies, the latter two backed by Russian airpower, will close in on the remaining territory held by the rebels and Syrian Kurds," Wayne White, former deputy director of the Middle East Intelligence Office at the State Department, told Xinhua.

The Trump administration's decision has thrown its Syria policy into chaos and also called into question America's commitment to stabilizing Iraq and Afghanistan, observed Kori Schake, deputy director-general of the International Institute for Strategic Studies, in an article published in The Atlantic.

"In the immediate future, all eyes will be on the details of the implementation of his (Trump's) decision as well as on the Turkish-Syrian border," said Bulent Aliriza, a senior associate at the Center for Strategic and International Studies, a Washington-based think tank.