London - One of the three attackers who killed seven people near London Bridge on Saturday night was previously investigated by British security services but had not been viewed as a serious threat, British police said on Monday.

Khuram Shazad Butt, aged 27, was a British citizen born in Pakistan, who was already known to police and Britain’s domestic spy agency MI5, London’s police force said. “However, there was no intelligence to suggest that this attack was being planned and the investigation had been prioritised accordingly,” police said in a statement.

The second attacker was named as 30-year-old Rachid Redouane, who police said claimed to be Moroccan and Libyan, and also went by the name Rachid Elkhdar with a different date of birth. Both men lived in the same area of east London.

Police said they were still working to establish the identity of the third attacker. Late on Saturday the three attackers drove south across London Bridge, mowing down pedestrians before stabbing bystanders in the nearby Borough Market area.

British police are stretched by the number of people they believe could potentially commit an act of terrorism. There are 500 current investigations involving 3,000 potential suspects. “A small number of the highest priority investigations involve current attack planning, and these investigations command a significant proportion of our resource,” police said.

Prime Minister Theresa May came under pressure from the media and the opposition Labour Party on Monday over cuts to police funding during the years when she was interior minister.

Saturday’s attacks - which in addition to the seven dead left dozens in need of hospital treatment, including 18 in a critical condition - came less than a week before Britons vote in a national election.

“Our work necessarily involves making difficult judgements about how to prioritise the resources available to us at a time when the UK is facing a severe and high tempo terrorist threat,” police said.

The aftermath of Saturday night’s rampage, which left seven dead and dozens wounded, dominated the campaign trail. Labour leader Jeremy Corbyn said he would support calls for May to quit, as she had overseen a sharp reduction in police numbers in her past job as interior minister.

The attack, claimed by the Islamic State group, saw three men wearing fake suicide vests use a white van to mow down people on London Bridge and then slash and stab revellers in Borough Market, a bustling late-night area. Armed police reacted swiftly, killing the attackers within eight minutes with 50 shots. Police said they carried out two early morning raids in east London on Monday and made “a number” of further arrests. Another 11 people were already in custody.

The capital’s police chief, Cressida Dick, said investigators had seized “a huge amount of forensic material” from the van.

“A very high priority for us is to try to understand whether they were working with anybody else,” she told BBC television.

Dick and Mayor Sadiq Khan visited London Bridge on Monday as commuters returned to the scene of the attacks after some security cordons were removed.

US President Donald Trump accused London Mayor Sadiq Khan on Monday of making a “pathetic excuse” over one of his comments following the attack that killed seven people in London on Saturday night.

“Pathetic excuse by London Mayor Sadiq Khan who had to think fast on his ‘no reason to be alarmed’ statement. MSM is working hard to sell it!”, Trump said in a Tweet. MSM referred to mainstream media.

Trump had faced a barrage of criticism on Sunday over an earlier Tweet that said: “At least 7 dead and 48 wounded in terror attack and Mayor of London says there is ‘no reason to be alarmed!’”.

No details have been released from the British authorities about the perpetrators. The Amaq news agency, which is affiliated with the IS group, said “the London attacks” were carried out by “a detachment of fighters from Islamic State”.

A Canadian and a Frenchman were among the fatalities and citizens of several nations were among the 48 injured, including Australia, Bulgaria, France, Greece and New Zealand.

Eighteen are still in hospital in critical condition, according to an update by Britain’s National Health Service.

French Foreign Minister Jean-Yves Le Drian was due to visit Britain on Monday to speak to the injured French nationals.

A vigil for the victims will take place at nearby Tower Bridge on Monday evening.

May blamed “evil” ideology and vowed to crack down on extremist content online, warning that attackers were “copying one another”.

She said the same ideology was behind the May 22 suicide bombing at a pop concert in Manchester that left 22 people dead, and the Westminster Bridge attack in March, which killed five.

Britain’s response to the terror threat must change, she said. Thirty-four people have died and around 200 injured in the three attacks since March.

“We cannot and must not pretend that things can continue as they are,” she said, adding there was “far too much tolerance of extremism in our country”.

But May’s own record came under fire from the Labour Party, which - according to opinion polls questioned for their reliability - has closed the gap on her Conservatives ahead of Thursday’s general election.

Campaigning resumed on Monday after being suspended for a day out of respect for the victims.

Labour leader Jeremy Corbyn noted that for six years, police numbers fell while May was in charge of security, implementing a budget-cutting drive under former premier David Cameron.

Asked by ITV television if he backed the calls for May to resign, he said: “Indeed I would.”

“There’s been calls made by a lot of very responsible people on this who are very worried that she was at the Home Office for all this time, presided over these cuts in police numbers and is now saying that we have a problem - yes, we do have a problem: we should never have cut the police numbers,” he said.

His party is calling for a drive to hire thousands of officers for neighbourhood duties, arguing that a grassroots approach will curb crime and radicalisation.

May insisted that London police were happy with their resources, while counter-terrorism budgets had been protected and the number of armed officers had increased.

Britain was already on high alert following the attack at a concert by US pop star Ariana Grande in Manchester, northwest England, in which seven children were among the 22 dead.

Grande headlined a benefit concert in Manchester on Sunday, alongside stars including Pharrell Williams and Justin Bieber.

The national threat level was raised to maximum after the Manchester attack and troops were deployed at key public sites, but reduced to its second-highest level last weekend.

Saturday’s rampage was the latest in a string of attacks to hit Europe, including in Paris, Berlin and Saint Petersburg.

Global leaders sent messages of support, though US President Donald Trump raised British hackles by attacking Khan on Twitter.

On Sunday, Trump misconstrued remarks the mayor had said in which he told Londoners that there was “no reason to be alarmed” by an increased police presence in the coming days.

In a notable contrast to Trump’s attack, the acting US ambassador in London, Lewis Lukens, commended Khan for his “strong leadership”.