- Envoy said it was vital to kill terrorists to stop them mounting attacks back home
- Comes after the remaining ISIS fighters in de facto capital fled after a standoff
- Thousands of people have left Europe to join the jihadists in Iraq and Syria
Foreign Isis fighters fleeing the group's fallen stronghold of Raqqa must be killed on the battlefield, according to a senior US adviser.
Brett McGurk, a top envoy for the American coalition fighting the terror group, said it was vital to kill foreign terrorists to stop them mounting attacks back home.
The comments come after the remaining Islamic State terrorists holed up in their de-facto capital fled after a final bloody standoff.
'Our mission is to make sure any foreign fighter who is here, who joined ISIS from a foreign country and came into Syria, they will die here in Syria,' Mr McGurk said.
'So if they're in Raqqa, they're going to die in Raqqa.'
The city's final days under Isis control were brutal, with 75 coalition airstrikes in 48 hours and a flurry of desperate terrorist car bombs.
Around 300 extremists hiding around a sports stadium and a hospital argued among themselves about whether to surrender, according to Kurdish commanders.
No government publicly expressed concern about the fate of its citizens who left and joined the Islamic State fighters plotting attacks at home and abroad.
In France, which has suffered repeated violence claimed by the Islamic State, Defence Minister Florence Parly was among the few to say it aloud.
'If the jihadis perish in this fight, I would say that's for the best,' Parly told Europe 1 radio last week.
The coalition has given names and photos to the Kurdish fighters to identify the foreign jihadis.
They are checking for wanted men among the dead or the few foreigners among the captured.
An official with the YPG Kurdish militia said foreigners who decided to fight until the end will be 'eliminated.'
No country will admit to refusing to take back citizens who joined the Islamic State, including women and their children.
But few are making much of an effort to recover them.
In Iraq, hundreds of Islamic State fighters have surrendered or have been taken into custody, and their families have been rounded up into detention camps.
The men are put on trial and face the death penalty if convicted of terrorism charges - even if they are foreigners. One Russian fighter has already been hanged.
Britain has not said how many of its former citizens are believed still fighting.
But one Briton posted a furious 72-minute monologue earlier this month from Raqqa as airstrikes and artillery fire boomed behind him.
He said Muslims around the world should be outraged at the treatment of Islamic State's followers.
'This is not me being an extremist. I'm a very moderate, mild person, hamdullah (thanks to God), and I find Islamic State to be very moderate and mild,' said the man.
He called himself Abu Adam al-Britani and was identified as Yasser Iqbal, a Porsche-driving lawyer who defended Islamic State's brutal practices as ordained by God.
He did not mention the group's routine public beheadings, enslavement of women or brainwashing of children to become hardened killers.
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