Hasakeh (Syria) (AFP) - The US-led coalition in Syria has begun withdrawing its troops, a spokesman said Friday, less than a month after US President Donald Trump announced the shock pullout.
It remained unclear how long it would take Washington to withdraw its forces, which have led the battle against the Islamic State group since 2014.
"CJTF-OIR has begun the process of our deliberate withdrawal from Syria," spokesman Colonel Sean Ryan told AFP in a statement, referring to the US-led anti-jihadist force.
"Out of concern for operational security, we will not discuss specific timelines, locations or troops movements," he said.
The Syrian Observatory for Human Rights reported that the coalition had started scaling down its presence at Rmeilan airfield in the Hasakeh province of northeastern Syria.
"On Thursday, some American forces withdrew from the Rmeilan military base," said Rami Abdel Rahman, the head of the Britain-based monitoring organisation.
He said some 150 US troops, around 10 armoured vehicles and some heavy equipment had left the base.
"This is the first such pullout of American forces since the US president's announcement" last month, he said.
The US-led coalition has several other bases across northeastern Syria, as well as in neighbouring Iraq, where Trump has said American forces will remain.
A US defence official in Washington had earlier confirmed to AFP that equipment was being removed from Syria.
- Pompeo visit -
The US-led coalition, which also includes countries such as France and Britain, was formed in mid-2014 to counter IS, which had seized swathes of Iraq and Syria and proclaimed a self-styled "caliphate".
Trump claimed last month that the jihadists had been defeated and that US troops could therefore come home.
Fighter jets and special forces have played key roles in efforts to claw back the territory lost to IS.
The coalition spokesman said the alliance's mission remained unchanged despite the pullout.
"CJTF-OIR's area of responsibility has changed, but our mission to ensure the enduring defeat of ISIS continues," Ryan said.
A Kurdish-led group, the Syrian Democratic Forces, is currently flushing the jihadists from the very last pockets of land they control in the Euphrates River Valley.
The battle against die-hard jihadists in remote areas along the Iraqi-Syrian border and the hunt for IS supremo Abu Bakr al-Baghdadi, the world's most wanted man, could last indefinitely.
The start of the drawdown coincided with a Middle East tour by US Secretary of State Mike Pompeo, who insisted in Cairo on Thursday that the withdrawal would go ahead despite widespread criticism.
On the same day however, Pompeo said in a speech that "when America retreats, chaos often follows."
- Turkish threats -
Earlier this week, US National Security Advisor John Bolton laid out conditions for the pullout, including the defeat of IS in Syria and guarantees for the safety of Washington's Kurdish allies, who have been threatened with an imminent offensive by Turkey.
Turkish President Recep Tayyip Erdogan labelled Bolton's comments unacceptable and a "grave mistake".
The People's Protection Units (YPG), which have spearheaded ground operations against IS, are a Syrian offshoot of the Kurdish PKK which has waged an insurgency against the Turkish state since 1984.
Turkey considers the YPG a terrorist movement and has repeatedly threatened to move into Syria to create a buffer zone along the border.
The group has already started reaching out to Damascus and its Russian sponsor.
Critics of Trump's decision, including within his own Republican party, have said a precipitous withdrawal would shatter US policy in Syria and allow IS to rebuild.
They have also argued that it would further allow regime ally Iran to extend its influence across Syria and potentially threaten Israel.
Since his surprise announcement last month, Trump has stressed any withdrawal would be coordinated, gradual and "prudent".
But observers have stressed that the announcement was having the same impact as the withdrawal itself.
"The damage is done," said Fabrice Balanche, a geographer and Syria expert.
"On the ground, the announcement of the pullout is as if they were already gone."