MI5 has begun an internal review over how it handled intelligence about the Manchester suicide bomber Salman Abedi amid growing criticism that it failed to deal properly with warnings that he posed a threat.
A security source told Reuters that Abedi was not among the 3,000 people currently under active investigation by MI5, although he was one of around 20,000 people "known" to the intelligence services.
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MI5 is subject to scrutiny by a committee of parliament, but "it is highly unusual for British authorities to make public that the security service is conducting its own internal investigation into possible lapses", says the news agency.
Home Secretary Amber Rudd told BBC News the review was the "right first step" for the intelligence agency to take, but declined today say what was known about Abedi and when.
It is not yet clear whether authorities became aware of the bomber during Theresa May's tenure as Home Secretary between 2010 and 2016.
Rudd was also forced to defend the use of new anti-terror powers after The Times reported that a "key" tool which gives law enforcement the power to stop Britons suspected of involvement in terrorist activity abroad at the UK border has only been used once it was introduced in 2015.