British counterterrorism police intensified investigations on Saturday into the man suspected of carrying out a deadly stabbing spree on London Bridge that killed two people.

Authorities said that the 28-year-old suspect had previously been convicted of terror-related crimes and was released from prison last year.

"This individual was known to authorities, having been convicted in 2012 for terrorism offences," Britain's top counterterrorism police officer, Neil Basu, said in a statement.

"Clearly, a key line of enquiry now is to establish how he came to carry out this attack," Basu said.

The man had been released "on license" in December last year, meaning he had to meet certain conditions or face going back to prison. British media reported that he agreed to wear an electronic ankle bracelet.

He'd been convicted in 2012 for his role in a plot to blow up the London Stock Exchange and reportedly had ties to radical Islamist terror groups.

Police searched a property in Staffordshire, north of Birmingham, where the suspect had been living.

Later on Saturday, "Islamic State" militants claimed that one of their "fighters" had carried out the attack.

Watch video 00:51 Police: London stabbing attack is 'terrorist incident'

Bystanders jump in to stop attack

Two people, a man and a woman, were killed in the attack. Three others were wounded and remain in hospital for treatment, authorities said.

The attack began around 2 p.m. local time on Friday at Fishmongers' Hall on the northern end of London Bridge. The suspect had been attending a prison education event at the hall before launching the attack.

The suspect, who was wearing what turned out to be a fake explosive vest, was tackled by bystanders on the bridge before police then shot and killed him.

Videos of the incident on social media showed several people restraining the man.

British authorities said they were treating the incident as a terror attack, but said they were not actively looking for other suspects.

Pressure on officials

The attack raises difficult questions for the British government and security services, as the attacker was already known to police and was possibly being monitored with an electric tag.

Brandon Lewis, junior interior minister, told BBC radio on Saturday that police will be looking into the conditions that were placed on the London Bridge suspect.

Watch video 00:29 Johnson: Anybody involved in this crime 'will be hunted down'

"There are conditions that are put on people in this situation and one of the things the police will be looking at is those conditions as part of that investigation," Lewis said.

British Prime Minister Boris Johnson said on Friday that "it is a mistake to allow serious and violent criminals to come out of prison early."

"It is very important that we get out of that habit and that we enforce the appropriate sentences for dangerous criminals, especially for terrorists," Johnson added.

The attack comes just weeks ahead of the UK general election on December 12.

The same area of London was targeted in June 2017 when three men drove a van into pedestrians on London Bridge before stabbing several people at bars and restaurants.

rs/rc (AP, AFP, dpa, Reuters)

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