British police have shot dead a man who had strapped a fake bomb to his body and stabbed several people on Friday, including two fatally, in what they said was a "terrorism incident" near the London Bridge area of the capital.
The attacker went on the rampage just before 2pm (14:00 GMT), targeting people at Fishmongers' Hall in the heart of the city's financial district.
Authorities identigied the suspect as 28-year old Usman Khan, who had been convicted of "terrorism" offences and was released from prison last year.
"This individual was known to authorities, having been convicted in 2012 for terrorism offences," the United Kingdom's top counter-terrorism police officer, Neil Basu, said in a statement. "Clearly, a key line of inquiry now is to establish how he came to carry out this attack."
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Two people - a man and a woman - were killed in the attack. In addition, a man and two women were injured and remain in hospital, Basu said.
Following the deadly incident, British Prime Minister Boris Johnson said on Friday it was important to enforce terrorism-related sentences.
"It is a mistake to allow serious and violent criminals to come out of prison early and 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 said.
A video posted on Twitter showed a group of about half a dozen men wrestling with someone on the ground on the pavement of the bridge during the attack. One of them backs away from the scene carrying a knife.
As he looks towards the melee, an armed police officer drags another person away from the man on the ground.
Soon after, what sounded like two gunshots rang out, and the man on the ground stops moving. Reuters could not immediately verify the footage.
In a statement on Twitter, London's Mayor Sadiq Khan said: "I remain in close contact with the Metropolitan Police and am being kept updated with events."
"It has been confirmed that people were injured in the attack. My heart goes out to them, their families and all affected," it said, adding that people must stay "resolute" and "united in the face of terror".
There was a heavy police presence in the area, which was sealed off as helicopters circled above. Several buildings were put on lockdown. People in buildings around the scene were evacuated to the north side of the River Thames by security services.
Connor Allen, an events manager who was near the scene, told Al Jazeera he heard "quite a few" gunshots.
"Everyone just started running, that's what you do in that situation," he said, describing scenes of "pandemonium".
The UK's main opposition Labour Party announced it would suspend all campaign events on Friday in light of the attack.
The ruling Conservative Party also stated it was unlikely that its events would go ahead on Saturday.
In a tweet, Labour leader Jeremy Corbyn posted: "Shocking reports from London Bridge. My thoughts are with those caught up in the incident. Thank you to the police and emergency services who are responding."
In June 2017, at least eight people were killed in the London Bridge area when attackers ploughed a van into pedestrians before carrying out a stabbing assault at Borough Market.
In March the same year, an attacker stabbed a policeman close to London's parliament buildings after a car ploughed into pedestrians on nearby Westminster Bridge.
Six people died, including the assailant and the policeman he stabbed, and at least 20 were injured in what police called a "marauding terrorist attack".
Earlier this month, Britain had lowered its national "terrorism" threat level to "substantial" from "severe", its lowest level since 2014.
