Alleged Islamic State 'Beatles' headed to US on charges of hostage deaths

Two alleged Islamic State militants known as the 'Beatles' will arrive in the United States on Wednesday to face trial on US criminal charges for their alleged involvement in beheadings of American hostages in Syria, the US Department of Justice said.

The alleged militants, Alexanda Kotey and El Shafee Elsheikh, have been under US military guard in Iraq for the last year and are now in FBI custody. They are due to appear in federal court in Alexandria, Virginia later on Wednesday, officials said.

The two grew up in Britain and were UK citizens, but the British government withdrew their citizenship. They are suspected of membership in a four-strong Islamic State cell known as the 'Beatles' because of their British accents.

That group is alleged to have detained or killed Western hostages, including US journalists James Foley and Steven Sotloff and aid workers Kayla Mueller and Peter Kassig. The cell became notorious for their alleged participation in graphic Islamic State videos posted online showing beheadings of foreign hostages.

"These charges are the product of many years of hard work in pursuit of justice for our citizens slain by ISIS. Although we cannot bring them back, we can and will seek justice for them, their families, and for all Americans," Attorney General William Barr said in a statement.

In order to secure British help in obtaining evidence on the pair, Barr agreed that US prosecutors would not seek the death penalty in any cases against them and would not carry out executions if they were imposed.

"As for their ringleader, Mohamed Emwazi (infamously known as Jihadi John), he faced a different type of American resolve - the mighty reach of our military, which successfully targeted him in an airstrike several years ago," Assistant Attorney General for National Security John Demers told a news conference.

The 24-page indictment includes a lengthy list of tortures which it accuses the defendants of inflicting on their captives, including electric shocks with a taser, forcing hostages to fight each other, 20-minute beatings with sticks and waterboarding.

Among specific murders the indictment alleges Kotey and Elsheikh were involved in was that of Mueller, who was seized and detained by Islamic State militants in August 2013. The indictment says that beginning about October 2014, Mueller was sexually abused by the late Islamic State leader Abu Bakr al Baghdadi while held captive in Syria.

Mueller's family received an email from Islamic State fighters in February 2014, confirming her death in Syria, the indictment says.

FBI Director Christopher Wray said Islamic State is still trying to radicalise people in the United States and elsewhere.

"Their goal is to motivate people to launch attacks against Western targets wherever they are, using any means available," Wray said.

Wray and Demers said the support of the British government was critical to moving the investigation and prosecution forward.

The families of Foley, Kassig, Mueller and Sotloff welcomed the news.

"James, Peter, Kayla and Steven were kidnapped, tortured, beaten, starved, and murdered by members of the Islamic State in Syria," they said in a joint statement.

"Now our families can pursue accountability for these crimes against our children in a US court."

The indictment alleges four counts of hostage taking resulting in death against Kotey and Elsheikh and four more criminal counts of conspiracy to murder and to support terrorists. If convicted, Kotey and Elsheikh could face up to life in prison.

As of Wednesday morning, a law enforcement official said, Kotey and Elsheikh did not have lawyers. There is an expectation among prosecutors that at least initially they will be represented by federal public defenders.