Two members of a notorious Islamic State cell that took hostage, tortured and killed four US citizens have been charged and are being brought to a federal court to face a judge for the first time, the US Department of Justice says.
El Shafee Elsheikh and Alexanda Kotey were allegedly members of a subgroup of the extremist militia - dubbed "The Beatles" for its four members' British accents - that tortured and killed a number of prisoners in Syria.
One of the cell's tactics was to behead civilians after making them kneel on the ground dressed in orange jumpsuits.
Videos of the killings were distributed via social media.
The accused will make their initial appearance in a federal court in Alexandria, Virginia, later in the day.
The two, who have been stripped of their British citizenship, were captured by US-backed Kurdish forces in Syria and were later transferred to holding cells in the Middle East.
As part of a deal with the UK, the US promised not seek the death penalty but the men could face life sentences.
The US made the pledge in order to obtain evidence held by British authorities.
The men are being charged with terrorism offences related to hostage taking and the killing of four US citizens, as well as citizens of the UK and Japan, said John Demers, an assistant US attorney general.
"Today is a good day but it is also a solemn one," Demers told reporters.
The leader of the cell was killed in an air strike in Syria while a fourth member was captured in Turkey.
The four US citizens killed by the IS cell were Jim Foley, Steven Sotloff, Peter Kassig and Kayla Mueller.
They were journalists and aid workers.
"Our message to other terrorists around the world is this: if you harm Americans, you will face American arms on the battlefield or American law in our courtrooms. Either way, you will be pursued to the ends of the earth until justice is done," Attorney General Bill Barr said in a statement.