“Every indication is that this was at the very least inspired by ISIS,” Pompeo said in an interview with CBS News, referring to the group by an acronym.

Sources familiar with internal US government reporting on the attacks told Reuters that while investigations are ongoing, US agencies believe the group that carried out the attacks had sympathies and possibly contacts with the Islamic State movement.

US agencies are collecting information on the attackers’ relationship with Islamic State and are trying to determine if there was any involvement in the attacks by what remains of the militant group’s central organisation, which scattered following its eviction from territory it controlled in Syria, the sources said.

One of the sources said official reporting supported news reports that the leader of the group that carried out the attacks is known as Mohammed Zahran Hashim and that he is the central unmasked figure in a photo of the alleged attack team issued by an Islamic State publicity outlet.

The source added that investigators believed another person involved in the attacks was Abdul Lathief Jameel Mohammed.  The Guardian reported that British counterterrorism investigators believed Mohammed attended a university in southeast England from 2006 to 2007.