Police investigating the Russell Square attack are focusing their lines of inquiry on mental health rather than terrorism , but are keeping an open mind regarding the motive.

A 19-year-old man has been arrested on suspicion of murder after a woman in her 60s was killed and is currently in police custody at a south London police station after being treated for his injuries in hospital.

Five others were injured, including two men and three women, with three of those having been discharged from hospital.

Police have now said that the man arrested is a Norwegian national of Somali ancestry and have search an address in north London and will search another in south London.

They have added that at this time they have found no evidence of radicalization or anything that would suggest the man in our custody was motivated by terrorism.

Police have also revealed that the woman who was killed is of American nationality, while those injured were Australia, American, Israeli and British.

In a statement, Assistant Commissioner Mark Rowley added: "We started to receive 999 calls from the public at 22:33hrs to reports of a man attacking people with a knife.

"Within six minutes of that call our armed officers were there; the man was Tasered and he was detained.

"Our firearms officers bravely rushed to that scene with very little information.

"They would not have known if this was an act of terrorism or the random attack we now know it be.

"They detained an armed and dangerous man - and resolved it using the minimum necessary force - no shots were fired.

"We should be proud of them and the British tradition of using the minimum necessary force."

In a press conference in the early hours of Thursday (August 4) morning, a Met Police spokesperson said that terrorism "remains but one line of enquiry for us to explore."

However, in an update police have now said that they are focusing their investigation on the suspect's mental health, but are retaining an open mind on the motive.

Mayor of London Sadiq Khan has told Londoners to "remain calm and vigilant" in the wake of the attack in a statement released on Thursday (August 4) morning.

The Metropolitan Police Service's Homicide and Major Crime Command is leading the investigation, supported by officers from the Counter Terrorism Command.

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."

Officers are continuing to interview witnesses and most of the cordons have been removed. One partial road closure remains in place.

Commissioner Sir Bernard Hogan-Howe said: "My thoughts are with the family of the woman who was murdered and those who were injured. A normal night out in our busy capital has ended in horrific circumstances.

"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 six 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.

"My thoughts, and those of his colleagues, are also with the officer who was seriously injured yesterday in a separate incident. One of my Flying Squad detectives remains in hospital after he was hit by a moped as two suspected robbers tried to flee after an attempted raid."

Anyone with information is asked to contact the incident room at Lewisham police station on 020 8721 4868 or if they wish to remain anonymous, Crimestoppers on 0800 555 111.