Fierce clashes erupted between US-backed Kurdish forces and ISIS militants in the latter's last toehold in Syria on Saturday, while Washington-backed rebel groups cracked down on ISIS sleeper cells in the country's south-east, a war monitor reported.
The UK-based Syrian Observatory for Human Rights said the Kurdish-led Syrian Democratic Forces (SDF) battled ISIS militants on the eastern flanks of the town of Hajin, on the eastern banks of the Euphrates River.
The SDF, backed by coalition warplanes, killed at least 19 ISIS fighters in the past 24 hours, the monitor said on Saturday.
Clashes erupted after ISIS launched a counterattack with the aim of recapturing the town of Hajin, which they lost to the SDF last week.
Saturday’s death toll brings the total number of ISIS fighters killed in the area since September to around 988, according to the monitor.
The ISIS attack, according to the SOHR, is the first on US-backed forces in east Syria since US President Donald Trump announced the withdrawal of around 2,000 American troops from the country on Wednesday.
Coalition warplanes, meanwhile, targeted ISIS positions on the eastern banks of the Euphrates with several air strikes the SOHR said on Saturday.
It was not immediately clear if a US exit would mean the end of air strikes against ISIS.
US officials told Reuters that the withdrawal means an end to the US air campaign, but US Secretary of State Mike Pompeo appeared to indicate otherwise. "The US intends to continue that counter-terrorism campaign, continue the fight against ISIS, whether it stems from Syria or other places," Mr Pompeo told Fox News in an interview.
The SDF has responded to Mr Trump's announcement by warning that a US withdrawal could lead to an ISIS resurgence. In a statement released on Thursday, the SDF said it would "have a negative impact on the counter-terrorism campaign".
"It will give terrorism … the momentum to recover and conduct a terrorist campaign in the region," the group said.
Turkish President Recep Tayyip Erdogan said on Friday that his country will take over the fight against remaining ISIS fighters.
Meanwhile, in south-eastern Syria, a US-backed rebel group cracked-down on an ISIS sleeper cell operating in the Rukban camp, near the Jordanian border.
The SOHR said that the Maghawir Al Thawra (MAT) rebel group arrested around 16 people suspected of being members of an ISIS sleeper cell operating within the camp.
The Baladi media network, which is affiliated with the Syrian opposition, said that the MAT group, backed by the US coalition, foiled an attempt by ISIS militants to infiltrate a US base in south-eastern Syria.
Maghawir Al Thawra, whose several hundred fighters work alongside US troops at the Tanf garrison, captured at least 14 fighters following clashes, according to Baladi.
US troops have not left the strategic Tanf garrison on the Iraq-Jordan border following Mr Trump's decision to pull out of Syria, the leader of the Maghawir Al Thawra rebel group said Saturday.
Colonel Muhanad Al Talaa said although they were notified of Washington's decision, the situation on the ground remained as it was.
"American troops plan to withdraw completely form Syria but I don't have details and things are as they are up until this moment," he told Reuters from the base.
Tanf is the only position with a significant US military presence in Syria outside the Kurdish-controlled north, where it has much larger air bases.