United States officials have pledged to hold terrorists accountable following the capture of two Britons suspected of having been part of the Islamic State extremist group dubbed "The Beatles".
Alexanda Kotey and El Shafee Elsheikh are currently being held in Syria after being captured by Kurdish militia fighters in January and a US Department of Defence (DoD) spokesman said they are "still considering options" for the pair.
Along with Mohammed Emwazi - the killer nicknamed Jihadi John - and Aine Davis, they are thought to have been part of a group named after the '60s band because of their English accents.
The four Londoners, now held by US-backed Syrian Democratic Forces (SDF), were linked to a string of hostage murders in Iraq and Syria during the bloody Islamist uprising.
US officials said the pair "are suspected to have participated in the detention, exploitation and execution of Western detainees".
Asked if they would be prosecuted and if so where they might face trial Major Adrian Rankine-Galloway from the DoD told the Press Association: "We are still considering options regarding el-Sheikh and Kotey, but rest assured our intention is to hold anyone accountable who commits acts like those they are alleged to have committed."
He said US Government agencies are working closely with coalition partners "on the disposition of detainees in SDF detention".
He confirmed they are being held in a "detention location" in Syria but said he could not give any further information.
Mark Campbell, co-chairman of the Kurdish Solidarity Campaign, said he understood from sources in the YPG (Kurdistan People's Protection Units) that the arrests had taken place in the Deir ez-Zur region in the north east of Syria, towards the Iraq border.
Bethany Haines, whose father David was killed in 2014 after being held captive for 18 months, told ITV's Good Morning Britain she would like the pair to be "locked up with the key thrown away" and is hopeful their capture will bring closure to bereaved families.
French journalist Nicolas Henin, who was held hostage by IS told BBC Radio 4's Today programme they should be returned to Britain to be "judged fairly in their home country" while Diane Foley, mother of murdered US journalist James, told the programme she would like them to be brought to trial in America.
Defence Secretary Gavin Williamson told The Times: "These are people who have done absolutely vile and despicable crimes and brought absolutely so much misery.
"It is good that they have been hunted down and caught."
The New York Times, which first broke the story of the capture, said Kotey, 34, and Elsheikh, 29, were identified by fingerprints and other biometric means.
It has been reported that they have had their British citizenship revoked - but this has not been confirmed by authorities in the UK.
In January 2017, US authorities named Kotey, from Paddington, as a member of the cell and said they had imposed sanctions on him.
In a statement at the time, the State Department said Kotey was "one of four members of an execution cell for ... the Islamic State of Iraq and the Levant (Isil)".
It said the "notorious cell, dubbed 'The Beatles'" had held captive and beheaded approximately two dozen hostages.
It went on: "As a guard for the cell, Kotey likely engaged in the group's executions and exceptionally cruel torture methods, including electronic shock and waterboarding.
"Kotey has also acted as an Isil recruiter and is responsible for recruiting several UK nationals to join the terrorist organisation."
The Kotey family have said they had "seen news about Alexe today", but said they would not be commenting further and asked that they are not contacted by the media.
Former child refugee Elsheikh, a mechanic from White City in west London, "was said to have earned a reputation for waterboarding, mock executions, and crucifixions while serving as an Isis jailer", the US State Department said.
Emwazi, who was killed in a US air strike in 2015, appeared in a number of videos in which captives including British aid workers Mr Haines and Alan Henning were beheaded.
The fourth member, Davis, was convicted of being a member of a terrorist organisation and jailed for seven-and-a-half years by a court in Silivri, Turkey, in May 2017.
The Foreign Office said it did not comment on individual cases or ongoing investigations.