04/08/2016 11:36 AM AEST | Updated 05/08/2016 6:48 AM AEST

London Knife Attack Leaves Woman Dead, Several Injured

An American woman was killed and five other people injured Wednesday when a man with suspected mental health issues went on a knife rampage in central London. Police said there was no evidence that the attack was related to terrorism.

Armed police were called at 10:33 p.m. local time after a Norwegian man of Somali origin attacked people with a knife in London’s Russell Square, an elegant park near the site of a 2005 suicide bombing.

The victim, identified by Scotland Yard late Thursday as 64-year-old Darlene Horton, a U.S. citizen from Florida, was treated at the scene but pronounced dead a short time later.

Horton’s husband, Richard Wagner, is a professor at Florida State University and spent the summer teaching FSU’s London Study Program. The two had planned to return home Thursday.

Another woman and four men were treated in hospital, though three of them were later discharged. Nationals from Australia, Britain, and Israel were also hurt.

”All of the work we have done so far increasingly points to this tragic incident as having been triggered by mental health issues,” said London Metropolitan Police Assistant Commissioner Mark Rowley.

“We believe this was a spontaneous attack and that the victims were selected at random. So far we have found no evidence of radicalization that would suggest that the man in our custody is in any way motivated by terrorism,” added Rowley, who is Britain’s most senior anti-terrorism officer. Initially he said that terrorism was a line of inquiry.

Police, who arrived within six minutes of being called, used a Taser electric shock gun while detaining the 19-year-old suspect. They later formally arrested him on suspicion of murder.

Neil Hall / Reuters
An armed police officer attends the scene of a knife attack in Russell Square in London, England, on Thursday.

Officers cordoned off the southern part of the square, which sits at the heart of London’s university area and is close to landmarks such as the British Museum, for several hours as forensics officers examined the attack scene.

Later, workmen hosed blood off the pavement.

London’s Sadiq Khan, the first Muslim mayor of a major Western capital, called for vigilance and urged Londoners to report anything suspicious to the police‎, who increased their presence in the capital.

“The safety of all Londoners is my number one priority and my heart goes out to the victims of the incident in Russell Square and their loved ones,” he said.

“I urge all Londoners to remain calm and vigilant. Please report anything suspicious to the police‎. We all have a vital role to play as eyes and ears for our police and security services and in helping to ensure London is protected.”

Hours before the Russell Square attack, London’s police chief said that he would deploy an additional 600 armed officers across the capital to protect against attacks.

London counter-terrorism police chiefs have previously warned that the Islamic State was seeking to radicalize vulnerable people with mental health issues to carry out attacks. In some operations, police commanders have taken advice from specialist psychologists.

Militants hit London with coordinated suicide bombings on July 7, 2005, killing 52 people. One of the bombs detonated on a bus close to Russell Square.

Since then, dozens of plots have been foiled and there have been smaller-scale attacks, such as the beheading of an off-duty soldier by militant Islamists in a London street in May 2013.

A man who attacked passengers at a London underground train station in December was jailed for life earlier this month. The judge said the attacker was suffering from paranoid schizophrenia at the time of the offense but may have been motivated by events in Syria.

This article has been updated to include new details, including the nationalities of those attacked, the identity of the stabbing victim and new comments from London police.