Part of yesterday's hike in the UK risk threat assessment is the fear that Abedi could have been working as part of a group of accomplices with possible links to militant groups who have the competence to plot and execute suicide bombings.

"The question is: Was he acting alone or was he part of a network of others who want to kill. That is what the investigation is focusing on," a source told Reuters adding that "the concern is that there may be others out there who helped him to make the bomb. Making a bomb of this sort requires a certain level of expertise and competence," the source said.

At an afternoon press conference, Manchester Chief Constable Ian Hopkins said it is clear "this is a network we are investigating." He declined to give any further details on the investigation.