LONDON — A member of the Islamic State extremist group who was part of a notorious quartet that orchestrated the beheadings of Western hostages in Syria has been identified, according to news reports.

The man, Alexanda Kotey, 32, is thought to be half Ghanaian and half Cypriot. He was part of the group nicknamed the Beatles, led by the Islamic State’s most infamous executioner, Mohammed Emwazi, better known as Jihadi John. Mr. Emwazi was killed in an American airstrike in November.

American officials could not be immediately reached to confirm the reports, which were published on Sunday by The Washington Post and BuzzFeed. A spokeswoman for Britain’s Home Office said she could “neither confirm nor deny” the reports.

The group is believed to have killed the American journalists James Foley and Steven J. Sotloff, and their beheadings were captured on videos in which Mr. Emwazi was seen reading a statement criticizing President Obama and the American military operation against the Islamic State in Iraq. The captors also beheaded the American aid worker Abdul-Rahman Kassig, previously known as Peter, as well as two Britons and a Japanese hostage.