Diehard jihadists have blocked roads out of the last scrap of their Islamic State group "caliphate" in Syria, US-backed forces fighting them said Sunday, preventing hundreds of civilians from fleeing.
US President Donald Trump called on his European allies to take back alleged jihadists captured in Syria, prompting Belgium to call for a "European solution" to the security issue.
IS declared a proto-state across parts of Syria and neighbouring Iraq in 2014, but has since lost all of it except a tiny patch of less than half a kilometre square in eastern Syria near the Iraqi border.
Near the front line in the village of Baghouz, the sound of outgoing mortar rounds punctured the otherwise quiet afternoon, an AFP correspondent there said.
There were a few bursts of gunfire from the Baghouz skyline and the thick whir of warplanes overhead.
On a rooftop on the edges of the village, a fighter with the US-backed Syrian Democratic Forces battling IS told AFP that even the frequencies used by the jihadists to communicate had gone dead.
"They used to ask for ammunition by saying: 'You have five crates of tomatoes. Bring them to us.' They spoke in code," Sheldar Hasakeh said.
"They wouldn't say they were under fire, they'd say 'It's raining on us from the north,'" said the stocky 40-year-old.
"Now their area of control is really squeezed and they don't have as many walkie talkies. They're not talking to each other as much," he added.
Earlier Sunday, SDF spokesman Mustefa Bali said IS had blocked roads out of its holdout, preventing up to 2,000 civilians from escaping.
"Daesh has sealed off all the streets," he said, using the Arabic acronym for IS.
A spokesman for the US-led coalition said IS was using these women and children as "human shields".
"Civilians who have escaped are reporting ISIS is using them as human shields," Sean Ryan said.
Thousands of people have streamed out of the so-called "Baghouz pocket" in recent weeks, but at a collection point for new arrivals on Sunday, dozens of tents and a few trucks sat empty.
"It's been two days since anyone came out," an SDF fighter told AFP.
After years of fighting IS, the SDF hold hundreds of foreigners accused of fighting for the group, and well as related women and children.
Syria's Kurds have repeatedly called for their countries of origin to take them back, but these nations have been reluctant.
The issue has taken on greater urgency, however, amid fears of a security vacuum since Trump's shock announcement in December that US troops would withdraw.
"The United States is asking Britain, France, Germany and other European allies to take back over 800 ISIS fighters that we captured in Syria and put them on trial," Trump said in a tweet, using another acronym for IS.
Otherwise, "we will be forced to release them. The US does not want to watch as these ISIS fighters permeate Europe, which is where they are expected to go."
Trump's tweet prompted a reaction from Paris, Brussels and Berlin.
In Syria, "it is the Kurds who hold them (the French jihadists) and we have every confidence in their ability to keep them detained," French junior interior minister Laurent Nunez said.
If they return, "they will all be tried, and incarcerated," he said, after France this month opened the door to bringing back its citizens.
A French source said an estimated 150 French nationals, including 90 children, could be brought back, but authorities have not confirmed any transfer.
In Belgium, justice minister Koen Geens called for a collective "European solution" that carries the least security risks.
In Germany, foreign ministry sources said "the federal government is examining options to enable German citizens to leave Syria, especially in humanitarian cases".
Beyond Baghouz, IS retains a presence in Syria's vast Badia desert, and has claimed deadly attacks in SDF-held territory.
"Over the past month, more than one foreign sleeper cell was arrested in multiple areas in Syria," spokesman Bali said.
Any withdrawal would leave Syria's Kurds exposed to a long-threatened attack by neighbouring Turkey, which views Kurdish fighters as "terrorists".
They have scrambled to seek a new ally in Damascus after spending most of Syria's conflict working towards self-rule.
Eight years into the conflict that has killed more than 360,000 people, President Bashar al-Assad's government controls nearly two-thirds of the country.
Assad on Sunday warned the Kurds that the US would not protect them against Turkey.
"No one will protect you except your state," he said.