LONDON - British police investigating Saturday's (June 3) attack in London have detained a "number of people" after entering two properties in early morning raids in the east of the city.

Police said officers from the Counter Terrorism Command unit said on Monday they had raided the properties and searches were ongoing in connection with the attack that killed seven people and injured more than 50 on Saturday night, Reuters reported.

Police earlier said they had detained 11 people following two other raids in east London.

The BBC on Monday reported police as saying they were aware of the identity of the three attackers, but would not be releasing details about them at this stage.

Police are working to establish whether the militants were supported by anyone else, the head of the city's police force told BBC TV.

"A very high priority for us obviously is to try to understand whether they were working with anyone else, whether anybody else was involved in the planning of this attack and to find out the background to it," London's Metropolitan Police chief Cressida Dick said.

"We've carried out searches in a variety of places in east London and we've seized a huge amount of forensic material, so we're working very quickly."

ISIS on Sunday claimed responsibility for the attack by the knife-wielding men who mowed down and stabbed revellers in London, before they were shot dead in a barrage of police gunfire. "A detachment of fighters from ISIS carried out London attacks yesterday," AFP reported, citing the Amaq news agency, which is affiliated with the extremist group.

The rampage at a popular nightlife hub around London Bridge by three men wearing fake suicide vests was the third deadly terror attack in Britain in less than three months and came only days before a general election.

British Prime Minister Theresa May will hold a meeting of the government's emergency security committee on Monday to discuss its response. May has blamed "evil" extremist ideology and vowed to crack down on extremist content online worldwide.

National campaigning for Thursday's vote was suspended for the day out of respect for the victims, who included 48 people treated in hospital for injuries.

Of those, 21 are still in a critical condition.

One Canadian national and one Frenchman were among the fatalities and seven French citizens were among the injured.

No details have been released about the perpetrators, who were shot dead within minutes by police.

POLICE 'WARNED ABOUT ATTACKER'

Britain's security services were in focus after media reports said some of the suspects may have slipped through the intelligence network. According to The Daily Mail, a friend of the attacker had reported him to an anti-terror hotline after he became radicalised through watching extremist YouTube videos. Police had also been warned after the suspect reportedly attempted to radicalise children in a local park, The Daily Mail and The Guardian reported.

Eight officers fired an "unprecedented" 50 rounds at the three attackers, according to Mark Rowley, head of national counter-terrorism policing, who said that a member of the public also suffered a gunshot wound.

Detectives were still investigating whether the assailants acted alone, and Rowley said their identities would be released "as soon as operationally possible".

Police launched raids in the ethnically diverse London suburb of Barking in the hours after the rampage, arresting seven women and five men aged between 19 and 60 at two properties.

A 55-year-old man was later released.

Copycat attacks

Theresa May said the attack was driven by the same "evil ideology" of extremism behind last week's Manchester suicide bombing that left 22 people dead, and the Westminster attack in March, which killed five.

"The recent attacks are not connected but we believe we are experiencing a new trend in the threat we face," she said after chairing an emergency ministerial meeting.

She warned that perpetrators are inspired to attack "by copying one another".

The assailants ran people over on London Bridge before lunging seemingly at random at the crowds gathered around Borough Market, which is full of restaurants and bars.

Gerard Vowls, 47, said he saw a woman repeatedly stabbed, and threw chairs, glasses and bottles at the attackers in a bid to stop them.

"They kept coming to try to stab me... they were stabbing everyone. Evil, evil people," he told The Guardian newspaper.

Another witness called Eric told the BBC he had seen three men get out of the van and thought they were going to help tend those who had been run over.

Instead they "started kicking them, punching them and took out knives. It was a rampage really," he said, adding that he heard a shout of: "This is for Allah".

An Australian was among those hospitalised, while a Spaniard escaped with light injuries.

French Foreign Minister Jean-Yves Le Drian is due to visit Britain on Monday to speak to the injured French nationals, after President Emmanuel Macron said France was "more than ever at Britain's side".

Among those stabbed was a London Transport Police officer, who was one of the first responders on the scene and received injuries to his face.

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

Praying for London

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

Grande, who headlined a benefit concert in Manchester on Sunday, alongside stars including Pharrell Williams and Justin Bieber, tweeted that she was "Praying for London".

"A lot of people suffered and I had some second thoughts coming, especially with what happened last night in London," ticket holder Abdullah Mala, 34, told AFP. "But we got to move on".

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.

Prime Minister Theresa May, who served as interior minister for six years before taking office after the Brexit vote last summer, said Britain's response to the terror threat must change.

"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." The ruling Conservatives and the main opposition Labour party suspended national campaign events for the day, but May insisted the election would go ahead as planned on Thursday.

Saturday's rampage is the latest in a string of attacks to hit Europe, including in Paris, Berlin and Saint Petersburg, and the French, German and Russian leaders sent messages of support.

United States President Donald Trump on Sunday called the London attack an "evil slaughter" and said the US would do everything it could in its power to assist Britain to bring those responsible to justice, Reuters reported. "This bloodshed must end. This bloodshed will end," Trump said in brief remarks after a gala event at Ford's Theatre in Washington.

Trump came under criticism earlier on Sunday after he lashed out at London's mayor Sadiq Khan, accusing him of downplaying the threat of terrorism after the latter said there was "no reason to be alarmed" over the greater security presence in the city following the attack.

"At least 7 dead and 48 wounded in terror attack and Mayor of London says there is 'no reason to be alarmed!'" he tweeted.

Khan, in an interview with the BBC shortly after the attack, had asked Londoners and visitors to be calm and vigilant. "You will see an increased police presence today, including armed officers and uniformed officers. There is no reason to be alarmed by this," he had said.