A man, who The Yorkshire Post is not naming, has been named as a key conspirator with Mohammed Emwazi - the killer given the moniker Jihadi John, and whose identity was already well known - following a joint investigation between the Washington Post and BuzzFeed News.
ITV subsequently named a second previously unidentified member of the quartet.
Both men are believed to be from London. There was no official confirmation of their names by the intelligence services, although the men have long been associated with Emwazi.
He was killed in a drone strike in Raqqa in November and was deemed responsible for the deaths of several hostages, including Britons Alan Henning and Yorkshire-born David Haines.
One of the men named by Buzzfeed and ITV has been mentioned in British court cases in connection with terror allegations as long ago as 2014. The drug dealer left England in 2013 to become an IS guard, ITV said. He was born in London with roots in Gambia, and later became interested in Islam, reports said.