The bomber who killed 22 people at a concert in the British city of Manchester had "likely" been to Syria, French Interior Minister Gerard Collomb said Wednesday (May 24th).

Collomb told BFMTV that British intelligence services had informed their French counterparts that Salman Abedi, of Libyan origin, "grew up in Britain and then suddenly, after a trip to Libya and then likely to Syria, became radicalised and decided to carry out this attack”.

Collomb said it was "possible" that Abedi had received assistance from other people, and noting that links with the "Islamic State of Iraq and Syria" (ISIS) were "proven", AFP reported.

ISIS has claimed responsibility for the attack on the concert by US pop star Ariana Grande in which many of the victims were children.

"At the moment we only know what British investigators have told us," Collomb said.

British interior minister Amber Rudd told BBC radio Wednesday it was "likely, possible" that the bomber "was not doing this on his own".

Rudd said the 22-year-old had been on the radar of the intelligence community.

After arresting a 23-year-old man on Tuesday, police said they had taken three more men into custody on Wednesday in south Manchester, where Abedi lived.

In the wake of the attack, Britain has raised its terror alert level to maximum for fear of an imminent new terror strike.