The woman who was murdered during a mass stabbing in central London's Russell Square has been identified as a US national, with the suspect described as a Norwegian of Somali origin. Police said the woman in her 60s was killed in a "spontaneous attack" in which the victims were "selected at random".

Police were called to reports of a man armed with a knife attacking people in Russell Square just after 10.30pm on 3 August. Armed officers arrived at the scene within five minutes and managed to detain the suspect after discharging a Taser.

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The 19-year-old was arrested on suspicion of murder after receiving treatment in hospital and is currently in custody at a South London police station. Following a raid on the suspect's house, police said there is no evidence of radicalisation or that the man was motivated by terrorism.

The Norwegian ministry of foreign affairs confirmed the suspect emigrated from the country to the UK in 2002. A spokesperson said: "We will assist the British police in the normal manner, with information and any requests they might have in their investigation."

The US woman was pronounced dead at the scene despite receiving "extensive treatment" by the London Ambulance service. Four others, revealed as an Australian, a Briton, an Israeli and another US citizen, also recieved non-life threatening injuries during the attack

Two of the injured victims remain in hospital while the other three have been discharged.

Police said that while they are retaining an open mind regarding the motive for the attack after suggesting terrorism could be a factor, they are now saying they will "focus our lines of inquiry on mental health".

Armed police have also been deployed across London as additional reassurance and security.

Russel Square
Police officers and cleaners attend the scene of a knife attack in Russell Square in London Neil Hall/ Reuters

Assistant Commissioner Mark Rowley, from the Metropolitan Police, said: "This was a tragic incident resulting in the death of one woman and five others being injured. Early indications suggest that mental health was a factor in this horrific attack. However, we are keeping an open mind regarding the motive.

"As a precautionary measure, Londoners will wake up this morning to notice an increased presence on the streets of officers, including armed officers today. We would urge the public to remain calm, alert and vigilant."

One eyewitness, Pol O'Geibheannigh, described "wall to wall" armed police and a woman on the floor following the attack. He told Sky News: "She was lying in a pool of blood with a red blanket on top of her. I went into the bar and it wasn't until an hour later that they put the tent up."

A second witness told BBC Radio 4's Today programme: "We saw a guy being lifted into a stretcher and we didn't realise just how bad it had been because a lot of people got hurt, it wasn't just that one guy. As we made our way around the corner, we saw the [suspect] on the ground and they had taped him off in a triangle. They left him on the ground for a while then as we were watching they slowly went over the put the handcuffs on."

Mayor of London Sadiq Khan is urging all Londoners to "remain calm and vigilant" following the attack while police continue their investigation. He added: "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.

"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. Our police officers are doing an incredibly difficult job on our behalf and they have my full support."

Russel Square
A forensics tent stands behind police tape after a knife attack in Russell Square in London Neil Hall/ Reuters

Met Police Commissioner Sir Bernard Hogan-Howe said his thoughts are with the family of the victim as well as the injured, describing how a"normal night out in our busy capital has ended in horrific circumstances".

He added: "Our investigation is moving very quickly and our detectives have been working hard throughout the night. As we have already made clear, mental health remains a substantial focus for our investigation.

"Every day in London, my officers patrol and carry out operations to catch criminals in the knowledge that they face risk and danger. I am proud that last night our specialist firearms officers were on the scene in minutes and, using only a Taser, detained the subject. That demonstrates our commitment to use force in a professional and proportionate way. Their swift response undoubtedly helped to prevent more people from getting injured.

"Across our capital today you will see more police officers, armed and unarmed, to reassure the public after recent events overseas. We will protect our Capital and those who live, work and visit our city."