The family of Steven Sotloff, an American-Israeli journalist murdered by the Islamic State group, said they were relishing seeing his killer face justice after the apparent executioner was named.

The masked IS militant dubbed "Jihadi John", believed to be responsible for beheading Western hostages, including Sotloff, was revealed by experts and the media to be Kuwaiti-born London computer programmer Mohammed Emwazi.

"The Sotloff family was informed of John's identity. This is one step on a long road to bringing him to justice," said Barak Barfi, the Sotloff family's spokesman, in a statement.

"If indeed Mohammed Emwazi is the man who executed Steve, the Sotloffs have full faith that the American intelligence community and law enforcement agencies will apprehend him.