They include a teenager who went to the same gym as Butt who said he was approached to join the Islamic State (IS) group, and a woman who told police she feared he was trying to radicalise children, The Times said.
May hit back by criticizing Corbyn, a pacifist who has opposed some security legislation in parliament and expressed reservations in the past about police responding to armed attackers with "shoot-to-kill" tactics.
Italy has expelled more than 40 people in the past two years who were suspected of extremist activities but for whom there was insufficient evidence to bring formal charges.
British Foreign Secretary Boris Johnson voiced concern over apparent security failings as at least one attacker from Saturday's three-man rampage in London had previously been identified as an extremist, even appearing in a 2016 television documentary. He was also known to use the name Rachid Elkhdar, and was understood to be in possession of an Irish identity card when he was shot dead by police. Neighbors identified Butt from the film's footage Monday, pointing to a scene in which he is shown participating in a provocative prayer session at Regents Park, near London's biggest mosque helping to display a black flag covered in white Arabic lettering similar to the one used by the Islamic State group, which took responsibility for the attack.
He said: 'I'm articulating a deep anger amongst those people that have seen 20,000 police officers lose their jobs, seen firefighters lose their jobs, seen ambulance crews unable to cope'.
Police received reports of a van speeding into pedestrians on London Bridge at 10:08pm (2108 GMT).
"The most likely outcome, in fact, would be simply to drive threatening communications underground, where they will be harder to expose and challenge", EFF said in a statement.
Police on Monday carried out fresh raids and arrested "a number of people" in east London after detaining 12 people a day earlier in the suburb of Barking. Although May's call lacked specifics, some in the technology industry called her response predictable in light of her previous efforts to expand the UK's surveillance authority.
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May blamed "evil" Islamist ideology and vowed to crack down on extremist content online, warning that attackers were "copying one another". The assault was the third attack in three months in which most of the assailants had been on authorities' radar at some point.
"We grieve the loss of our lovely, loving daughter and sister".
Christine Archibald is pictured in this handout photo. She lived this belief, working in a shelter for the homeless until she moved to Europe to be with her fiance. She had room in her heart for everyone and believed strongly that every person was to be valued and respected. "Please honour her by making your community a better place". "They are going to have to look very closely at the communications of lots of people", he said.
Saturday's attack came less than two weeks after a suicide bomber Salman Abedi blew himself up at a concert in Manchester on May 22.
'Police services have become much more efficient, ' she said, adding: 'In the face of this changing threat, I will be seeking for London and for policing generally more resourcing'.
Meanwhile, large concrete barriers have been installed at Waterloo, Lambeth and Westminster bridges in London.
But May's own record came under fire from Labour, which - according to opinion polls questioned for their reliability - has closed the gap on her Conservatives ahead of Thursday's election.
May said Sunday that police had recently foiled five other plots.
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