A US-backed force in Syria said Tuesday it has arrested jihadists suspected of involvement in the deadliest attack on US troops since they deployed in the war-torn country in 2014.
Nineteen people including four American personnel were killed in the January 16 suicide bombing claimed by the Islamic State group in the northern Syrian city of Manbij.
The four Americans killed were two soldiers, a civilian defense department employee and a Pentagon subcontractor.
The US Department of Defense had previously reported only two American personnel killed in combat in Syria, in separate incidents.
A spokesman for the Kurdish-led Syrian Democratic Forces said that several suspects have been detained over the Manbij bombing.
"A group of suspects believed to be involved in (the) January 16 Manbij bombing that killed several US and SDF servicemen were captured following technical surveillance by our forces," Mustefa Bali said in English on Twitter.
The spokesman's comments came as his force advanced against the jihadists in eastern Syria, confining holdout fighters to a tiny slither in the village of Baghouz on the banks of the Euphrates River.
The Kurdish-led force on Sunday said at least 520 IS fighters have been captured in "special operations" by the SDF since January 9.
An additional 5,000 jihadists who have fled their last redoubt have been detained over the same period, it said.
After sweeping across swathes of Syria and Iraq in 2014, the ISIS jihadists' cross-border "caliphate" has been whittled down by multiple offensives to the tiny embattled enclave in Baghouz.
But despite the stinging defeats, ISIS has proved it is still capable of carrying out deadly attacks using hideouts in the sprawling desert or sleeper cells in the towns.
Run by a Washington-backed town council since the US-led coalition and its ground partners pushed out jihadists in 2016, Manbij has been a realm of relative quiet.
The town was considered sufficiently secure that a group of top US military commanders and lawmakers strolled through its market without body armour last summer.
President Donald Trump in December announced he would pull all American troops from Syria, claiming IS had been "largely defeated".
But the White House has since said it would maintain a small "peace-keeping" force of 200 US troops in the country.