US-backed Syrian forces said on Sunday that they were struggling to cope with a mass movement of foreigners from the ISIS territory and urged governments to take responsibility for their citizens.
The Kurdish-led Syrian Democratic Forces have moved nearly 5,000 men, women and children from the militants' last hold since Wednesday, stepping closer to retaking the last sliver of territory under ISIS control.
"The number of foreign fighters and their relatives that we are holding is increasing drastically," Kurdish foreign affairs official Abdel Karim Omar said. "Our current infrastructure can't handle the mass influx."
Syria's Kurds have repeatedly called on foreign countries to repatriate their citizens, but most have been reluctant to allow battle-hardened fighters and their relatives home because of security concerns.
At the height of its rule, ISIS imposed its brutal interpretation of Sharia in territory across Syria and Iraq that was about the size of the UK.
But more than four years after ISIS declared a cross-border "caliphate", the extremists have lost all but a tiny patch of land, mostly in the village of Baghouz near the Iraqi border.
After years of fighting ISIS, Syria's Kurds say they hold hundreds of fighters and their relatives.
"As thousands of foreigners flee Daesh's crumbling caliphate, the burden that is already too heavy for us to handle is getting even heavier," SDF spokesman Mustefa Bali said on Twitter late Saturday.
"This will remain as the biggest challenge awaiting us unless governments take action and fulfil their responsibilities for their citizens."
No evacuations were reported from the enclave on Saturday, but two batches of people that left on Wednesday and Friday included Europeans, Iraqis and nationals of former Soviet countries, the SDF said.
About 46,000 people, including a large number of foreigners, have streamed out since early December, the Syrian Observatory for Human Rights said.
While civilians are trucked north to Kurdish-run camps for the displaced, suspected extremists are sent to SDF-controlled prisons.
Mr Omar said that SDF detention centres could not accommodate all of the fighters coming from the last ISIS pocket.
The move to safety of men, women and children has put a strain on Kurdish-run camps for the displaced, especially Al Hol, which now shelters more than 40,000 people.
On Thursday, nearly 2,500 people arrived at the camp, worsening already dire conditions inside the crammed settlement, the UN's humanitarian co-ordination office said.
"Thousands more are expected in coming hours and days at Al Hol camp, putting a further strain on basic services," the UN agency tweeted on Friday.
"This sudden influx presents huge challenges to the response – additional tents, non-food items, water and sanitation and health supplies are urgently needed."
The International Rescue Committee on Friday said 69 people, mostly children, had died on the way to Al Hol, or shortly after arriving in past weeks.
The SDF said it was trying to evacuate move out civilians through a corridor before pressing on with a battle to crush the militants unless holdout fighters surrender.
About 2,000 people are believed to remain inside Baghouz, including foreigners.
Many European countries are now considering whether to bring back their citizens who travelled to join the group and prosecute them at home, or bar them from entry because of security concerns.
On Friday, the family of Shamima Begum, 19, said it would challenge the British government's decision to revoke her citizenship.
Ms Begum, who travelled to Syria in 2015 at the age of 15, was at risk of being stateless after Britain revoked her citizenship, and Bangladesh, from where her parents originated, said it did not want her.
On Thursday, the father of Hoda Muthana, 24, sued to bring her home after President Donald Trump's administration declared she was not a US citizen.
The battle for Baghouz is now the only live front in Syria's war, which has killed more than 360,000 people and displaced millions since 2011.
Further north, more than 20 civilians were killed on Sunday in central Syria when a landmine left by ISIS exploded under a van, the state news agency Sana reported.
The ordnance in the town of Salamiyeh killed farm workers who were heading to pick truffles in Hama's countryside.
Meanwhile, the UK said it fired its new Brimstone missile from a Eurofighter Typhoon fighter jet in Syria at an ISIS boat.
The British military said late last week that the Typhoon hit its target while on a mission over the Euphrates River area this month.
The UK’s fleet of Typhoon jets, a stalwart of the British Royal Air Force, was only upgraded to carry the Brimstone missile in January.
The addition of the weapons system was designed to prolong the life of the ageing jet as it neared retirement.
The Royal Air Force has reportedly used the new missile on missions in Iraq, Afghanistan and Libya.