An American woman has been killed and five people wounded by a man armed with a knife in London's Russell Square.
Police said the 19-year-old suspect was a Norwegian of Somali origin, but they have found no signs of radicalization. He was subdued by police using a Taser stun gun, London police said.
"Early indications suggest that mental health was a factor in this horrific attack," Assistant Commissioner Mark Rowley said in a statement.
"However we are keeping an open mind regarding the motive and terrorism remains one line of inquiry being explored."
Wednesday night's attack was less than a mile from the British Museum.
The name of the victim, believed to be in her 60s, was not released. Two other women and three men — British, American, Israeli and Australian — sustained non-life-threatening injuries, police said. Three were later discharged from the hospital, according to police.