U.S.-backed Kurdish fighters have captured two fugitive British Islamic State converts — part of a group of four terrorists known for torturing and beheading Westerners, U.S. officials say.

The officials identify the two as Alexanda Kotey and El Shafee el-Sheikh.

Kotey "likely engaged in the group's executions and exceptionally cruel torture methods, including electric shock and waterboarding," the State Department has said.

It also said el-Sheikh "earned a reputation for waterboarding, mock executions and crucifixions while serving as an ISIS jailer." ISIS is an acronym for the militant group.

U.S. officials said the Syrian Democratic Forces captured the two in eastern Syria in January.

The wanted men were part of a group of four Islamic State terrorists dubbed "The Beatles" because of their British accents. They operated out of Raqqa, the former self-declared IS capital in Syria.

The four became notorious for beheading their Western hostages and posting the grisly videos on social media.

The ringleader, known has "Jihadi John," was killed in a 2015 coalition airstrike. A fourth member, Aine Davis, is in a Turkish prison.