Video report by ITV News Correspondent Neil Connery
The families of murdered hostages have condemned complaints from two Britons accused of being members of a notorious IS death squad.
Alexanda Kotey and El Shafee Elsheikh, who are said to have been members of the brutal "Beatles" quartet of executioners in Syria and Iraq, have said they cannot get a fair trial because the UK Government stripped them of their citizenship.
They also described the execution of hostages as "regrettable" as they spoke to the Associated Press from a cell in northern Syria.
The daughter of British aid worker David Haines, who was held hostage and killed by the group, said the pair had shown "no remorse".
"As for them saying they have been stripped of rights, well when they held my father for 18 months with his family not knowing whether he was dead or alive, they stripped him of his rights," Mr Haines' daughter Bethany said In a statement.
"In my opinion they should be given an orange jumpsuit and stripped of all the things they hold dear and left to rot in Guantanamo Bay."
American journalist James Foley was also killed by the IS cell in 2014.
His mother Diane said: "They deserve to be held in solitary confinement for the rest of their lives and held accountable for the pain they've inflicted."
Kotey and Elsheikh were captured in January in eastern Syria by the Kurdish-led, US-backed Syrian Democratic Forces.
Along with Mohammed Emwazi - the killer nicknamed Jihadi John - and Aine Davis, Kotey and Elsheikh - a former child refugee - are thought to have been part of a group named after the '60s band because of their English accents.
The four Londoners were linked to a string of hostage murders in Iraq and Syria during the bloody Islamist uprising and gained global notoriety.
Emwazi, who was killed in a US airstrike in 2015, appeared in a number of videos in which captives including Mr Haines and Alan Henning were beheaded.
Davis was convicted of being a member of a terrorist organisation and jailed for seven-and-a-half years at a court in Silivri, Turkey, in May 2017
Elsheikh told AP the "illegal" revocation of the pair's citizenship exposes them to "rendition and torture".
He added: "Being taken to any foreign land and treated in anyway and having nobody to vouch for you.
"When you have these two guys who don't even have any citizenship...if we just disappear one day, where is my mum going to go and say 'where is my son?'"
He added they could also have "no fair trial, when I am 'the Beatle' in the media".
Though they spoke of their membership of IS, they did not admit to belonging to the cell or to have been involved in any of the kidnappings or killings. Elsheikh called the allegations "propaganda."
Asked about the beheadings of American journalist James Foley and other victims, Kotey said many in IS "would have disagreed" with the killings "on the grounds that there is probably more benefit in them being political prisoners."
"As for my position, I didn't see any benefit. It was something that was regrettable," he added. He also blamed Western governments for failing to negotiate, noting that some hostages were released for ransoms.
The pair's capture sparked a row over whether they should be returned to the UK for trial or tried where their alleged crimes were committed.
Last month Home Secretary Amber Rudd has left the door open to putting the British men on trial in a UK court.
The Home Secretary said she was "absolutely convinced and absolutely committed" to the idea of them "facing justice".
It was understood the pair had been stripped of their British citizenship, although officials at the Home Office refused to comment on individual cases at the time.