About 400 Islamic State members -- including foreign fighters -- have in recent weeks surrendered to US-backed forces in the jihadists' former Syrian stronghold Raqa, a US military official said Tuesday.

Colonel Ryan Dillon, a spokesman for the US-led coalition helping train and equip local forces in Syria and Iraq, said the bulk of those jihadists had surrendered over the past week, as operations to seize the city reached their final moments.

The fighters had surrendered to the Syrian Democratic Forces (SDF), a US-backed alliance of Kurdish and Arab fighter.

"In the last few days, about 350 fighters surrendered to the SDF in Raqa, with several confirmed foreign fighters taken into custody after SDF screening," Baghdad-based Dillon told reporters in a video call.

In recent weeks, an average of about four IS fighters had been surrendering each week, he added.

The SDF announced they had fully captured Raqa after more than four months of fighting.

"We have seen also that prior to these battles, once the area is isolated and before offensive operations begin, many of the leaders will often high-tail and leave," Dillon said.

When asked what the US military footprint would be in Raqa going forward, Dillon said there remained considerable work to do in the city.

"We must clear the remnants of all the explosives that have been left in Raqa throughout this battle," he said.

A Raqa security force commander and two colleagues were killed Monday as they walked through the city and triggered a bomb, Dillon said.

Elsewhere, the anti-IS coalition remains engaged in northern Iraq, particularly in the Anbar region, where allied aircraft have conducted more than 30 strikes in the past week.

IS still holds two towns in this area near the Syrian border -- Al-Qaim and Rawa.

In the strategic Iraqi city of Tal Afar, seized by Baghdad in August, IS abandoned large weapons caches including 550 homemade bombs, Dillon said.

Source: AFP