Syria war: Last of British IS 'Beatles' gang captured by Kurds

Two British men believed to be members of a notorious Islamic State group cell have been seized by Syrian Kurdish fighters, US officials say.

Alexanda Kotey, 34, and El Shafee Elsheikh, 29, were the last two members of the cell to remain at large.

The four, all from London, were nicknamed "the Beatles" because of their British accents.

US officials said the "execution cell" had beheaded at least 27 hostages and tortured many more.

Families of the men's victims have called for the two seized men to go on trial. Diane Foley - whose son James, an American journalist, was captured and beheaded by IS - told BBC Radio 4's Today programme she wants the men to face life imprisonment.

"Their crimes are beyond imagination," she added.

Nicolas Henin, a French journalist who spent 10 months as an IS captive, also told Today that he wanted justice. He stressed that any attempt to deny the men of their civil rights would only feed IS's claims of victimisation by the West.

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The latest arrests were confirmed by US officials.

Officials quoted by US media said the two men had been captured by members of the US-backed Syrian Democratic Forces (SDF), who are targeting remnants of IS.

The UK Foreign Office, meanwhile, said it did not comment on individual cases or investigations.

Their capture was first reported by the New York Times, who noted that American officials had wanted to keep the news secret.

The aim was "to allow analysts more time to pursue the intelligence leads developed from their detention and prepare raids against unsuspecting Islamic State targets", the newspaper said.

The Syrian fighters who apprehended them told US officials in mid-January that the two may have been captured, and the men's identities were later confirmed using fingerprints and other biometric data.

The families of the men told the BBC they were not aware of the capture until the story was reported by news organisations.

The Islamic State group's self-declared caliphate - its area of control - shrunk rapidly last year.

In October, the group lost its "capital" of Raqqa to the SDF. In the beginning of November, it lost Deir-al Zour in Syria on the same day as it lost al-Qaim in Iraq.

The SDF is an alliance of Kurdish and Arab fighters opposed to IS. The US-backed group has played a key role in driving IS from its strongholds in Syria.

The US has said it aims to maintain an open-ended military presence in the country to ensure the jihadist group's defeat.

However, the presence of large numbers of Kurdish armed forces in northern Syria has alarmed neighbouring Turkey.

Gordon Corera, security correspondent

The pair are said to have provided valuable intelligence following their capture. That may be helpful in answering the wider question of what happened to the foreign fighters as the so-called caliphate disintegrated.

How many of the thousands of foreign fighters were killed and how many went to other countries or would seek to come home? These men will have been priority targets - but not the only ones.

Their capture also raises the issue of what happens next. They could be put on trial in the US, since they were allegedly involved in the killing of US hostages - but there may be some in the Trump administration who would like to send them to Guantanamo Bay.

And it is not clear if this is - formally - an issue for the UK Government, as there are reports the pair may have had their UK citizenship stripped from them using powers available to the Home Office.

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