AL-OMAR OIL FIELD BASE, Syria >> The offensive on the last enclave held by the Islamic State group in eastern Syria has been blunted by the discovery of hundreds of civilians still living there, a commander with the Kurdish-led force fighting the extremists said today.

The U.S.-backed force known as the Syrian Democratic Forces, or SDF, launched the offensive to liberate the IS-held village of Baghouz a week ago, after more than 20,000 civilians, many of them foreign wives of IS militants, were evacuated through a corridor from the area in the eastern province of Deir el-Zour.

In Washington, President Donald Trump said the White House will make an announcement about Syria and the fight against IS by Saturday. His did not give details but his comments contrasted with the picture painted by SDF commanders, who said the battle has been progressing slowly.

“We have a lot of great announcements having to do with Syria and our success with the eradication of the caliphate and that will be announced over the next 24 hours,” Trump told journalists at the White House.

Adnan Afrin, the Kurdish commander, told The Associated Press that in the last three days IS militants brought up hundreds of civilians from underground tunnels to make the SDF and U.S.-led coalition aware of their presence.

He estimated that around 1,000 civilians, including women and children, are still in the area. He added that militants were hiding among them and using them as human shields.

“This was a surprise. We did not imagine there would be this number of civilians left,” Afrin said.

He said they were likely to be families of IS militants, but their discovery nonetheless has blunted the offensive. “We do not want to cause a massacre against civilians in the last (IS) pocket,” he said.

A blitz of airstrikes and shelling last week was believed to signal the end of the campaign against IS in its last toehold in Syria. Thousands of people, including many foreign fighters and their families, emerged from the area amid ferocious fighting as the SDF closed in from three sides under the cover of airstrikes by the U.S.-led coalition.

IS militants are now clinging to their last square kilometer (mile) of land in Baghouz. The anticipated declaration of victory against the group, however, has been delayed by this discovery of a large number of civilians in the area.

The Britain-based Syrian Observatory for Human Rights, a war monitor, reported late today that a convoy of seven trucks, three ambulances and other vehicles including Humvees for the U.S.-led coalition headed toward the IS-held area. The group said it believes that the aim is to draw out the remaining IS gunmen and their families.

“The convoy is likely to come back with at least 200 Islamic State group members of different nationalities,” the Observatory said, adding that it was not clear if they would agree to surrender. Hundreds of IS fighters have surrendered over the past weeks and were apprehended by members of the U.S.-led coalition and SDF fighters.

Organized access to the front line has been restricted for journalists amid security concerns, particularly after the injury of an Italian photographer earlier this week.

U.S.-backed forces are now conducting precision operations targeting the militants’ outposts in and around the village of Baghouz and working to clear surrounding villages of remaining fighters, SDF officials said.

The capture of Baghouz and nearby areas would mark the conclusion of a devastating four-year global campaign to end the extremist group’s hold on territory in Syria and Iraq, their so-called “caliphate,” which at the height of the extremists group’s power in 2014 covered nearly a third of both Iraq and Syria.

President Donald Trump has said the group is all but defeated. He announced in December that he would withdraw the 2,000 American troops in Syria.

It is not clear whether the Islamic State group is holding any civilian prisoners in the enclave, beyond their own families.

“We aim to save any prisoners, but we have no information about them. They can be among the civilians, or in underground prisons, we have no information,” said Afrin, the SDF commander.

The Observatory said SDF fighters discovered late Thursday the bodies of 26 IS gunmen who were killed in recent clashes near Baghouz.

The group added that some families of IS members tried to flee Thursday night into areas held by the SDF but did not succeed.

The DeirEzzor 24, an activist collective that covers events in eastern Syria, reported that U.S.-led coalition warplanes struck several suspected IS positions outside Baghouz today. It added that SDF fighters sporadically shelled the IS-held area.

The Kurdish Hawar news agency, meanwhile, reported that SDF fighters advanced slowly on the northern parts of Baghouz village because of the large number of mines and explosives planted by the extremists, who it said were also using civilians as human shields.

Hawar added that SDF fighters discovered an arms depot and a clinic used for treating IS gunmen.

Syrian opposition activists also reported that SDF spokeswoman Lilwa Abdullah escaped an assassination attempt Thursday when gunmen opened fire at her car as she drove between Deir el-Zour and the northeastern province of Hassakeh.

Also today, the Syrian government sent aid for the first time into the town of Hajin, which until recently was held by IS before it was recaptured by the SDF, Syria’s state news agency SANA reported.

SANA said the convoy made it today in coordination with Russia, which has been a main backer of the Syrian government. Hajin is on the east bank of the Euphrates River, while Syrian government forces and their allies are based its the west bank.