Armed officers shot and killed a man who injured three people in a "terrorist-related" stabbing attack in south London, the Metropolitan Police Service said Sunday. Authorities said the suspect, a 20-year-old, had a fake bomb strapped to his body and he had been "under active police surveillance" prior to the incident.

"Three people are known to have been injured in the #Streatham attack earlier this afternoon," the Met said on Twitter. One person was taken to the hospital in life-threatening condition, but has improved; a second person treated at the scene before being hospitalized and released. The third victim has non-life-threatening injuries, according to police.

Police shot the man at around 2 p.m. local time in the Streatham High Road area of London and he was later pronounced dead. Eyewitness Daniel Gough told BBC News he "heard three gunshots go off and everyone around me started running up a side street."

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"After a few minutes I went back down and saw a policeman and he yelled, telling everyone to get back," Gough said. "His gun was pointing in the direction of a man on the floor."

The London Ambulance Service said medics were on the scene within four minutes.

The Met said earlier the incident "has been declared as terrorist-related."

In a late Sunday update, Met Deputy Assistant Commissioner Lucy D'Orsi said officials are "confident" that the attacker was 20-year-old Sudesh Amman. She also confirmed the man was recently released from prison where he was serving time for terrorism offenses. Police said the incident was an isolated incident.

U.K. Prime Minister Boris Johnson thanked first responders and said his "thoughts are with the injured and all those affected."

Police said there was no "continuing danger" to the public, but the area remained closed as the investigation continued.

A witness on the scene said armed police were blocking off streets around Streatham High Road.

Something major happening in Streatham High Road. Armed police and roads closed off. pic.twitter.com/UDJL6On3TJ — 🎵🎶Andy Bullemor 🦂 (@andybullemor) February 2, 2020

In November, a stabbing on London Bridge left two people killed and three wounded. The attacker, who was wearing a hoax explosive device, was also shot and killed by police, who called the attack a "terrorist incident."