US president Donald Trump has threatened to release “thousands” of Isis fighters held in Syria “to Europe” if their countries do not take back their citizens who went to join the terror group.

Around 800 Isis fighters of European origin are currently being detained in northern Syria by the US-backed Syrian Democratic Forces, along with thousands of women and children.

The Trump administration has been pressuring EU governments to repatriate their citizens suspected of joining Isis, but most have been reluctant to do so, fearing they would present a security risk upon their return.

“We have thousands of Isis fighters that we want Europe to take and let’s see if they take them. And if they don’t take them, we’ll probably have to release them to Europe,” Mr Trump said on the White House lawn on Thursday.

The SDF is thought to be holding around 13,000 foreigners suspected of Isis links — not including Iraqi or Syrian fighters. That number is made up of 2,000 men and 11,000 women and children, most of whom were detained when the terror group’s caliphate fell earlier this year.

Timeline of the Isis caliphate Show all 19 1 /19 Timeline of the Isis caliphate Timeline of the Isis caliphate ISIS began as a group by the merging of extremist organisations ISI and al-Nusra in 2013. Following clashes, Syrian rebels captured the ISIS headquarters in Aleppo in January 2014 (pictured) AFP/Getty Timeline of the Isis caliphate Abu Bakr Al-Baghdadi declared the creation of a caliphate in Mosul on 27 June 2014 Timeline of the Isis caliphate Isis conquered the Kurdish towns of Sinjar and Zumar in August 2014, forcing thousands of civilians to flee their homes. Pictured are a group of Yazidi Kurds who have fled Rex Timeline of the Isis caliphate On September 2 2014 Isis released a video depicting the beheading of US journalist Steven Sotloff. On September 13 they released another video showing the execution of British aid worker David Haines Timeline of the Isis caliphate The US launched its first airstrikes against Isis in Syria on 23 September 2014. Here Lt Gen William C Mayville Jnr speaks about the bombing campaign in the wake of the first strikes Getty Timeline of the Isis caliphate Isis militants sit atop a hill planted with their flag in the Syrian town of Kobani on 6 October 2014. They had been advancing on Kobani since mid-September and by now was in control of the city’s entrance and exit points AFP/Getty Timeline of the Isis caliphate Residents of the border village of Alizar keep guard day and night as they wait in fear of mortar fire from Isis who have occupied the nearby city of Kobani Getty Timeline of the Isis caliphate Smoke rises following a US airstrike on Kobani, 28 October 2014 AFP/Getty Timeline of the Isis caliphate YPG fighters raise a flag as they reclaim Kobani on 26 January 2015 VOA Timeline of the Isis caliphate Isis seized the ancient Syrian city of Palmyra on 20 May 2015. This image show the city from above days after its capture by Isis Getty Timeline of the Isis caliphate Kurdish forces are stationed on a hill above the town of Sinjar as smoke rises following US airstrikes on 12 November 2015 AFP/Getty Timeline of the Isis caliphate Kurdish forces enter Sinjar after seizing it from Isis control on 13 November 2015 AFP/Getty Timeline of the Isis caliphate Iraqi government forces make the victory sign as they retake the city of Fallujah from ISIS on 26 June 2016 Getty Timeline of the Isis caliphate Iraqi forces battle with Isis for the city of Mosul on 30 June 2017 AFP/Getty Timeline of the Isis caliphate Members of the Iraqi federal police raise flags in Mosul on 8 July 2017. On the following day, Iraqi prime minister Haider Al Abadi declares victory over Isis in Mosul Getty Timeline of the Isis caliphate Members of Syrian Democratic Forces celebrate in Al-Naim square after taking back the city of Raqqa from Isis. US-backed Syrian forces declare victory over Isis in Raqqa on 20 October 2017 after a four-month long campaign Getty Timeline of the Isis caliphate Female fighters of the Syrian Democratic Forces celebrate in Al-Naim Square after taking back the city of Raqqa from Isis. US-backed Syrian forces declare victory over Isis in Raqqa on 20 October 2017 after a four-month long campaign AFP/Getty Timeline of the Isis caliphate Trucks full of women and children arrive from the last Isis-held areas in Deir ez-Zor, Syria in January 2019 They were among the last civilians to be living in the ISIS caliphate, by this time reduced to just two small villages in Syria’s Deir ez-Zor Richard Hall/The Independent Timeline of the Isis caliphate Zikia Ibrahim, 28, with her two-year-old son and 8-month-old daughter, after fleeing the Isis caliphate, on Saturday 26 January 2019 Richard Hall/The Independent

More than 50 British citizens are thought to be detained, including nine men, 20 women and around 30 children. Shamima Begum, who fled her home in Bethnal Green aged 15 to join Isis in Syria, is among them.

Mr Trump appeared to conflate the European fighters with Isis members from other countries in his comments on Thursday, claiming there were “2,500 Isis fighters that we want Europe to take, because they were going back into Europe, into France, into Germany, into various places.”

The president was responding to a question from reporters about Tulsi Gabbard, a Democratic congresswoman from Hawaii running for the White House in 2020.

It is not the first time Mr Trump has threatened to release European Isis fighters held in Syria. Back in February, when the Isis caliphate was close to collapse, he called on “Britain, France, Germany and other European allies to take back over 800 Isis fighters that we captured in Syria and put them on trial.”

“The caliphate is ready to fall. The alternative is not a good one in that we will be forced to release them,” he wrote on Twitter.

The SDF, the US-backed militia that is holding the suspects, has said it does not have the capability to continue holding them indefinitely. It has proposed setting up an international tribunal to try the Isis suspects.

But such a court would need the backing of the United Nations Security Council, and would likely be blocked by Russia on behalf of its ally, the Syrian government, which sees the SDF as a threat to its rule.

In the meantime, US military leaders have warned that the next generation of jihadis was being raised in Syrian camps holding the families of Isis members.