Salman Abedi, the suspected bomber behind Wednesday's attack at a pop concert in Manchester, had been on the radar of security services, interior minister Amber Rudd confirmed on Wednesday.
"It is somebody that they had known and I'm sure when this investigation concludes we'll be able to find out more," she told BBC radio.
Rudd confirmed that bomber Abedi, a British man of Libyan heritage who died in the explosion on Monday night, had been on the radar of the security services.
"We do know that he was known up to a point to the intelligence services," she told Sky News.
Clarifying this on the BBC she said: "The security services will know a lot of people. It doesn't mean that they're expected to arrest everybody they know.
"But it is somebody that they had known." She said she had "complete confidence" in the security services.
The minister said she was "not surprised at all" that the attack had been claimed by the Islamic State group, but said there was no information yet to confirm the extremist organisation's active direction.
Meanwhile, French interior minister Gerard Collomb said that Abedi had "likely" been to Syria.
He told BFMTV that British intelligence services had told their French counterparts that 22-year-old Abedi, who was 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".
Earlier, media reports gave out key details about 22-year-old Abedi.
Who was Abedi?
Abedi, the suicide bomber who killed 22 people in Manchester, was a business student who dropped out of university.
Born to a devout Muslim family from Libya, he was brought up in Britain's third biggest city. Newspapers said he was known to the security services, and The Financial Times reported that he had turned to radical Islam in recent years.
Abedi, 22, worshipped at a suburban mosque where his father was well known, and even occasionally performed the call to prayer.
He was named by police and Prime Minister Theresa May the day after the deadly attack, which left dozens wounded. "The perpetrator was Salman Ramadan Abedi, who was born and brought up in Britain," May said, condemning his actions as "callous and cowardly".
Media reports said Abedi's parents fled Libya to escape the regime of former dictator Muammar Gaddafi.
Around 16,000 Libyans live in Britain, and Manchester is home to the largest community, according to the BBC. It was a focus of celebrations when the Gaddafi regime fell in 2011.
Reports said the suicide bomber was the second youngest of four children, including another son and one daughter.
One member of Manchester's Libyan community told The Guardian newspaper, "He was such a quiet boy, always very respectful towards me. His brother Ismael is outgoing, but Salman was very quiet. He is such an unlikely person to have done this."
Abedi had recently returned from Libya, according to The Times newspaper's front page on Wednesday, which cited a school friend as saying that he left three weeks ago and returned in the last few days.
Police said they were urgently seeking to establish whether Abedi worked alone, or acted as part of a larger network.
Abedi's family were closely linked to the Didsbury Mosque, a Victorian former Methodist chapel in a leafy suburb that was bought in 1967 by donors from the Syrian Arab community.
His father Ramadan had sometimes performed the call to prayer and his brother Ismael had been a volunteer. One senior figure from the mosque Mohammed Saeed told The Guardian that when he once gave a sermon denouncing terror, Abedi stared him down. "Salman showed me a face of hate after that sermon," Mohammed Saeed said of the 2015 encounter. "He was showing me hatred."
May raises threat level to 'critical'
Prime Minister May raised the UK's terror threat to the "critical" level, which means an attack is imminent, and deployed army in the key sites. May said the decision to raise the threat level was taken after security forces were unable to rule out if Abedi was behind Monday's suicide bombing in Manchester, acted alone. The move will see the army deployed to secure the country's key sites.
"It is a possibility that we cannot ignore, that there is a wider group of individuals linked to this attack," May said.
The terror threat level has been raised to its highest level of "critical", meaning further attacks may be imminent, she said.
It is for the first time in 10 years the feared threat of a terror attack has reached its highest level. Up to 5,000 soldiers will be deployed on Britain's streets as a result of the move.
The Islamic State terror group had claimed responsibility for the bombing and warned of more attacks.
With inputs from agencies
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Updated Date: May 24, 2017 14:17:30 IST