BAGHOUZ: US-backed Syrian forces were sweeping on Thursday through the final enclave that had been held by Islamic State fighters and said they would declare the group defeated once a search for hidden mines and jihadist holdouts was complete.

"Our forces are still conducting combing and search operations and as soon as they are finished we will announce the liberation," Mustafa Bali, spokesman for the Syrian Democratic Forces, said in a note to journalists.

Bali told Reuters the operation included sweeping for mines and combing for fighters still hidden in trenches and tunnels beneath Baghouz, the last patch of Islamic State territory.

The last clashes reported by the SDF were on Tuesday, indicating that major fighting is over in the last big battle of a five-year international campaign against a self-proclaimed caliphate that once comprised a third of both Iraq and Syria.

The SDF, backed by US air power, swept on Tuesday into a camp where hundreds of fighters had been making their last stand with thousands of civilians, many their own wives and children.

The situation in Baghouz appeared calm for a second consecutive day, a Reuters journalist in Baghouz said. Warplanes with the US-led coalition, including drones, could be seen overhead.

A news outlet with close ties to the Syrian Kurdish-led authorities, Hawar, reported that the operation was now finished and Islamic State defeated. But an SDF denial swiftly made clear it was not quite prepared to declare victory yet.

The International Rescue Committee (IRC) said another 2,000 women and children had arrived late on Wednesday at the al-Hol camp in northeastern Syria that has received tens of thousands of people who have poured out of the shrinking Islamic State territory.

"These women and children are in the worst condition we have seen since the crisis first began. Many have been caught up in the fighting and dozens have been burnt or badly injured by shrapnel," Wendy Taeuber, IRC’s Iraq and northeast Syria country director, said in a statement.

"We are expecting another 3,000 to arrive soon and we are very worried that they may be in even worse shape."

The camp is now holding more than 72,000 people, including more than 40,000 children, IRC said. The total number of deaths on the way to al-Hol or shortly after arriving there now stood at 138, the overwhelming number of the babies and infants.

Though the defeat of Islamic State at Baghouz ends its grip overpopulated territory, it remains a threat, with fighters operating in remote territory elsewhere and capable of mounting insurgent attacks.

The US military has warned that Islamic State may still count tens of thousands of fighters, dispersed throughout Iraq and Syria, with enough leaders and resources to present a menacing insurgency.

US Secretary of State Mike Pompeo, on a visit to Jerusalem, told reporters victory was "close".

He was proud of "the work that the United States did, the Department of Defense did, that the folks fighting down in the Euphrates river valley did," he said. "The threat from radical Islamic terrorism remains. We need to finish out the last few square metres there, in Syria. Still, work to do."

The Pentagon's internal watchdog released a report last month saying Islamic State remained an active insurgent group and was regenerating functions and capabilities more quickly in Iraq than in Syria.

It warned the group could resurge in Syria within six to 12 months and regain limited territory without sustained pressure.

The United States believes Iraq is the location of its leader Abu Bakr al-Baghdadi, who stood at the pulpit of the great medieval mosque in Mosul in 2014 to declare himself caliph, sovereign over all Muslims.