The suicide bomber who killed 22 people and wounded 59 after a pop concert in Manchester was known to the security services and likely did not act alone, interior minister Amber Rudd said on Wednesday.
Rudd also said it was "irritating" that information about the investigation into the bombing had been leaked by U.S. security sources before the British police were ready to go public with it.
Police have named the bomber as Salman Abedi, 22, who was born in Manchester to parents of Libyan origin.
"It seems likely, possible, that he wasn't doing this on his own so the intelligence services and the police are pursuing their leads in order to make sure they get all the information … that they need to keep us safe," Rudd told BBC radio.
Asked if he was known to the intelligence services, she said: "the security services will know a lot of people, it doesn't mean they are expected to arrest everybody that they know but it is somebody that they had known before and I'm sure when this investigation concludes we'll be able to find out more."
Rudd was asked about the fact that lots of information about Abedi, including his name, had come out from the United States and whether she would look again at information sharing with other countries.
"Yes, quite frankly. I mean the British police have been very clear that they want to control the flow of information in order to protect operational integrity, the element of surprise, so it is irritating if it gets released from other sources and I have been very clear with our friends that should not happen again."
Asked whether the U.S. leaks had compromised the investigation, she said: "I wouldn't go that far but I can say that they are perfectly clear about the situation and that it shouldn't happen again."
