By Ellen Francis
BEIRUT (Reuters) - The U.S. decision to withdraw from Syria will allow Islamic State to regroup at a critical stage in the conflict, Washington's Kurdish partners said on Thursday, after Western allies expressed alarm at the sudden move.
The U.S.-backed Syrian Democratic Forces (SDF) said President Donald Trump's withdrawal of all U.S. troops would also leave Syrians stuck between "the claws of hostile parties" fighting for territory in the seven-year-old war.
Trump's announcement on Wednesday upended a central pillar of American policy in the Middle East and stunned U.S. lawmakers and allies, who challenged the president's claim of victory.
The U.S. president defended his decision on Thursday. In a series of tweets, Trump said he was fulfilling a promise from his 2016 presidential campaign to leave the Middle Eastern nation. The United States was doing the work of other countries, including Russia and Iran, with little in return and it was "time for others to finally fight," he wrote.
The SDF, supported by roughly 2,000 U.S. troops, are in the final stages of a campaign to recapture areas seized by Islamic State militants.
But they face the threat of a military incursion by Turkey, which considers the Kurdish YPG fighters who spearhead the force to be a terrorist group, and possible advances by Syrian forces - backed by Russia and Iran - committed to restoring President Bashar al-Assad's control over the whole country.
After three years of fighting alongside U.S. forces, the SDF said the battle against Islamic State had reached a decisive phase that required more support, not a precipitate U.S. withdrawal.
Western allies including France, Britain and Germany also described Trump's assertion of victory as premature.
Officials said France will keep its troops in northern Syria for now because Islamic State militants have not been wiped out and pose a threat to French interests.
"For now, of course we are staying in Syria because the fight against Islamic State is essential," Europe Minister Nathalie Loiseau said.
France has about 1,100 troops in Iraq and Syria providing logistics, training and heavy artillery support as well as fighter jets. In Syria it has dozens of special forces, military advisers and some foreign office personnel.
A British junior defence minister said on Wednesday he strongly disagreed with Trump. "(Islamic State) has morphed into other forms of extremism and the threat is very much alive," Tobias Ellwood said in a tweet.
PUTIN SEES NO PULLOUT YET
Islamic State declared a caliphate in 2014 after seizing large swathes of Syria and Iraq. The hardline group established its de facto capital in the Syrian city of Raqqa, using it as a base to plot attacks in Europe.
According to U.S. estimates, the group oversaw about 100,000 square kms (39,000 square miles) of territory, with about 8 million people under Islamic State control. It had estimated revenues of nearly $1 billion a year.
A senior U.S. official last week said the group was down to its last 1 percent of the territory it once held. It has no remaining territory in Iraq, although militants have resumed insurgent attacks since the group's defeat there last year.
Russian President Vladimir Putin said he largely agreed with Trump that Islamic State had been defeated in Syria, but added there was a risk it could regroup.
He also questioned what Trump's announcement would mean in practical terms, saying there was no sign yet of a withdrawal of U.S. forces whose presence in Syria Moscow says is illegitimate.
Israel will continue to act "very aggressively against Iran's efforts to entrench in Syria," Israeli Prime Minister Benjamin Netanyahu said.
Neighbouring Turkey, which has threatened an imminent military incursion targeting the U.S.-allied Kurdish YPG fighters in northern Syria, has not commented directly on Trump's decision, although an end to the U.S.-Kurdish partnership will be welcomed in Ankara.
Kurdish militants east of the Euphrates in Syria "will be buried in their ditches when the time comes", state-owned Anadolu news agency reported Defence Minister Hulusi Akar as saying.
Turkey considers the YPG a terrorist group and an extension of the outlawed Kurdistan Workers Party (PKK).
Turkey has intervened to sweep YPG and Islamic State fighters from parts of northern Syria that lie west of the Euphrates over the past two years. It has not gone east of the river, partly to avoid direct confrontation with U.S. forces.
(Additional reporting by Daren Butler in Istanbul and John Irish in Paris; Writing by Dominic Evans; Editing by Janet Lawrence)