Two notorious ISIS militants dubbed "The Beatles" who were held by Kurdish-led fighters in Syria are now in US custody and have been moved out of the country, President Donald Trump said early Thursday.
Turkey has launched an assault on the Syrian Kurdish forces -- with which the US partnered to combat ISIS extremists -- sparking fears that the offensive could lead to captured fighters.
"In case the Kurds or Turkey lose control, the United States has already taken the 2 ISIS militants tied to beheadings in Syria, known as the Beetles, out of that country and into a secure location controlled by the US," Trump tweeted.
"They are the worst of the worst!"
The pair, El Shafee Elsheikh and Alexanda Amon Kotey, were part of an extremely violent all-British four-man cell that kidnapped and tortured foreigners, including journalists, at the height of the terrorist group's power in Syria and Iraq.
A US defense official had earlier confirmed they had taken custody of two "high-value" ISIS individuals from the Kurdish-led Syrian Democratic Forces (SDF).
"They have been moved out of Syria and are in a secure location," the official said, without identifying where. "They are being held in military custody pursuant to the law of war."
One other member of the four-man militant cell was killed in a drone strike and the fourth is imprisoned on terror charges in Turkey.
Their cell is accused of abducting and decapitating around 20 hostages including American journalist James Foley, who was beheaded in 2014.
The beheadings, often carried out on camera, horrified the world soon after ISIS took over much of Iraq and Syria in 2014.
Trump had earlier said the US was taking steps to prevent the potential escape of particularly dangerous ISIS extremists amid the Turkish offensive.
The SDF have been holding prisoner some 10,000 captured ISIS militants.
The SDF-held extremists include more than 2,000 of foreign nationality, many of them from Europe.
Trump said the Kurds were still guarding many of the ISIS militants, but also said Turkey would be responsible for them.
Trump and other US officials have repeatedly pressed other nations across Europe and the Middle East to take back the detainees from their countries. But international leaders have been largely reluctant and have been slow to take any back.