BAGHDAD -- After days of conflicting statements about a timeline for President Donald Trump's decision to withdraw American forces from Syria, a U.S. defence official said Friday the process has begun with the removal of some military cargo.

The official said the movement of equipment is part of what the military calls a "deliberate withdrawal" from Syria, where some 2,000 troops have been working with a coalition of Syrian Kurdish and Arab fighters to defeat the remnants of the Islamic State group.

The official, who spoke on condition of anonymity to discuss details that have not yet been publicly announced, provided no numbers, but said the equipment withdrawal is underway and that an unspecified number of additional U.S. troops have been brought into Syria to assist with the process, including by providing additional security.

Hours earlier, Col. Sean Ryan, spokesman for the U.S.-led coalition fighting the Islamic State group, said "the process of our deliberate withdrawal from Syria" has started. He said the U.S. would not discuss a specific timeline, locations or troop movements out of concern for operational security.

There has been confusion over plans to implement Trump's pullout order and threats from Turkey to attack the Kurdish fighters, who Ankara views as terrorists because of their ties to insurgents within Turkey.

Earlier this week, the U.S. National Security Adviser John Bolton said American troops will not leave northeastern Syria until IS is defeated and American-allied Kurdish fighters are protected, signalling a slowdown in Trump's initial order for a rapid withdrawal.

The Britain-based Syrian Observatory for Human Rights, which monitors the conflict in Syria through a network of activists on the ground, said the withdrawal began Thursday night. It said a convoy of about 10 armoured vehicles, in addition to some trucks, pulled out from Syria's northeastern town of Rmeilan into Iraq.

A senior Kurdish politician said the Kurds are aware of the U.S. beginning the withdrawal, describing it as "America's decision."

"The Americans have a right to make decisions that are in their country's security and national interests," said Ilham Ahmed, who co-chairs the U.S.-backed Syrian Democratic Council in northeastern Syria.

She added that the peace and stability of areas U.S. forces withdraw from "must be guaranteed," including by putting an end to the Turkish threats and fully eradicating the Islamic State group and its sleeper cells.

There are 2,000 American troops in Syria. Trump's abrupt decision in December to pull them out, declaring in a tweet the defeat of IS, sent shockwaves across the region and prompted a flurry of criticism from some of his generals and national security advisers. It led to the resignation of U.S. Defence Minister James Mattis and the top U.S. envoy to the anti-IS coalition. It also led to major criticism that the U.S. was abandoning its local Kurdish allies amid Turkish threats of an imminent attack.

Bolton, on a visit to the region this week, said the U.S. pullout was conditional on defeating IS and guarantees that the Kurds would be protected. His statements appeared to contradict those made earlier by Trump. Secretary of State Mike Pompeo, who is on a tour of the region, has also sought to reassure the Kurds that they will be safe after U.S. troops withdraw from the country.

"These have been folks that have fought with us and it's important that we do everything we can to ensure that those folks that fought with us are protected," Pompeo said of the Kurds while visiting Irbil, the capital of Iraq's semi-autonomous Kurdish region, after talks in Baghdad.

After initially tweeting about the decision to bring back U.S. troops "now," Trump this week said "we will be leaving at a proper pace while at the same time continuing to fight ISIS and doing all else that is prudent and necessary!"

Kurdish officials, meanwhile, have demanded clarifications from the U.S. over its intentions. A U.S. troop pullout leaves the Kurds exposed to Turkish forces on one side and Syrian government troops on the other. The withdrawal benefits Syrian President Bashar Assad and his international backers, Russia and Iran, who are primed to move into the region to fill a vacuum left behind by the Americans.

On an unannounced visit to troops stationed near the Syrian border Friday morning, Turkey's Defence Minister Hulusi Akar reiterated Ankara is "determined" to fight Kurdish militias it considers terrorists and said military preparations were ongoing.

"When the time and place comes, the terrorists here will also be buried in the ditches and trenches they have dug," the minister said in southern Sanliurfa province. He spoke before the announcement on the U.S. withdrawal and did not address it.

Russia's Foreign Ministry spokeswoman Maria Zakharova said the Americans are not serious about withdrawing from Syria.

Speaking to reporters in Moscow on Friday, she said it appears the U.S. "is looking for a reason to stay." She said Russia has not seen public statements laying out the U.S. strategy in Syria and so cannot be sure that the U.S. is serious about leaving.

U.S. troops have been involved in Syria's war since 2014, when the first elite forces arrived in the country to advise Kurdish-led fighters battling the Islamic State group.

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Karam reported from Beirut. Associated Press writers Bassem Mroue in Beirut, Nataliya Vasilyeva in Moscow, Zeynep Bilginsoy in Istanbul and Robert Burns in Washington, DC, contributed to this report.

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This story has been corrected to show that the U.S. has begun withdrawing equipment but not troops from Syria.