Police have said a knife attack that left an American woman dead and five others injured is not believed to be terror-related.

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Police were called just after 10.30pm to reports of a man armed with a knife assaulting people in Russell Square.

Armed units arrived at the scene around five minutes later and Tasered and detained the suspect.

Six people were injured during the incident, including the woman who died at the scene. Two other women and three men were hurt.

The suspect, a 19-year-old man, has been arrested on suspicion of murder and remains in custody.

Investigators said interviews, searches and intelligence reviews gave no indication the Norwegian national, of Somali origin, was radicalised or motivated by terrorism.

In pictures: Russell Square stabbing Show all 6 1 /6 In pictures: Russell Square stabbing In pictures: Russell Square stabbing A police forensic officer at work in Russell Square, central London, after a knife attack in which a woman in her 60s was killed and five people were injured. PA In pictures: Russell Square stabbing A police forensic officer at the scene in Russell Square, central London PA In pictures: Russell Square stabbing A private ambulance leaves Russell Square in London early on August 4, 2016, after a woman in her 60s was killed during a knife attack AFP/Getty Images In pictures: Russell Square stabbing Police at the scene of a stabbing attack in Russell Square in central London on August 4, 2016 AFP/Getty Images In pictures: Russell Square stabbing A police officer lays flowers left by a member of the public close to the scene where one women died and several people were injured in a knife attack in Russell Square EPA In pictures: Russell Square stabbing The police cordon Russell Square in central London on August 4, 2016, AFP/Getty Images

A spokesperson for the Metropolitan Police said early indications suggested that mental illnes was a "significant factor" in the case.

Assistant Commissioner Mark Rowley said: “As a precautionary measure, Londoners will notice an increased presence on the streets of officers, including armed officers today. We would urge the public to remain calm, alert and vigilant.”

The Mayor of London, Sadiq Khan, said police were working to keep the capital safe and establish the "full facts".

“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 added.

“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.