The US expects every country will work to take back their citizens who fought for Islamic State in Syria, US Secretary of State Mike Pompeo said on Wednesday during a visit to Britain.
Earlier this year Britain removed the citizenship of a teenager who travelled to join Islamic State.
The case illustrated the difficulties Western capitals are facing as they try to work out what to do with battle-hardened foreign jihadist fighters, and their wives and children.
Asked during a news conference with British Foreign Secretary Jeremy Hunt whether he was frustrated by Britain's reluctance to take back its foreign fighters, Pompeo said: "We have an expectation that every country will work to take back their foreign fighters and continue to hold those foreign fighters, we think that is essential."
US President Donald Trump has urged Britain, France and Germany to take back more than 800 captured Islamic State fighters and put them on trial.
Pompeo said he discussed the issue with Iraqi leaders during a visit to Baghdad on Tuesday, and countries should work together to ensure that the West would "never have to fight these same terrorists again".
"We have rounded them up, they are now contained and they need to continue to be contained so they cannot present additional risk to anyone anywhere in the world," he said.