The US-backed Syrian Democratic Forces (SDF) began on Sunday its assault against the last bastion of the Islamic State (IS) militant group in Syria where it is located in Baghouz.

After controlling a third of the territory in Iraq and Syria, the SDF call Baghouz the last remnant of the ‘caliphate,’ which was declared by IS in 2014.

According to Reuters, the offensive was launched on Sunday against IS fighters holed up in the village of Baghouz on the banks of the Euphrates River near the Syria-Iraq border.

Intense artillery and rocket fire continued into the night on Sunday as US-backed fighters in the Kurdish-led SDF maintained their assault, AFP reported, adding that warplanes and drones targeted the village as explosions were heard and fires were seen from intense artillery and rocket fire.

Mustafa Bali, the head of the SDF media office, told Reuters on Sunday that no civilians or surrendering IS fighters had emerged from Baghouz since Saturday. “The military operations have started,” Bali said later in the day, adding that “our forces are now clashing with the terrorists and the attack started.”

The SDF waited outside Baghouz for weeks before launching the assault so that civilians could be evacuated. Many are wives and children of IS fighters, AFP reported, adding that there are also their hostages, such as the Yazidi women who have been held hostage for years.

Aid agencies are struggling to cope with the thousands of weak and hungry people who have fled Baghouz. There were many more people in the village, many living in tents, than had been anticipated.

It is still not known how many fighters, or civilians, are still in Baghouz, the UN said. Some estimates suggest 500 fighters and up to 4,000 women and children could still be there.

Since December, nearly 59,000 people have left the IS-held territory, according to the Syrian Observatory for Human Rights.

Despite the assault on Baghouz, IS maintains a presence in Syria’s vast Badia desert and has claimed a series of deadly attacks in SDF-held territory.

Last week, among the IS fighters detained and civilians placed in displacement camps are a number of foreign nationals. Jens Laerke, the spokesperson of the UN Office for the Coordination of Humanitarian Affairs, said that the camps now hold at least 45,000 people many of them had arrived while exhausted, hungry, and sick.