Five other people were wounded in the attack, including another American, an Israeli and an Australian.
An American woman was killed in a knife rampage by a 19-year-old attacker in London on Wednesday night, U.K. police confirmed.
The woman is described as being in her 60s, Metropolitan Police Assistant Commissioner Mark Rowley said in a press conference early Thursday.
Five other people were wounded in the attack, including another American, an Israeli and an Australian. Two victims remain in the hospital.
Rowley said the attacker, a Norwegian national of Somali origin, appears to be mentally ill and that police investigators have found no connection to radical Islam or terrorism.
The British press quickly reported fears that the attack was linked to ISIS after a string of deadly attacks in France, Belgium and Germany that have shocked Europe.
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However, Rowley said: “I emphasize that so far we have found no evidence of radicalization that would suggest the man in our custody is in any way motivated by terrorism.”
He added: “At this time, we believe this was a spontaneous attack and that the victims were selected at random.”
Armed officers rushed to the scene of the attack in Russell Square in northwest London and Rowley praised their bravery for confronting the attacker, not knowing whether the incident was part of a wider terrorist attack.
The officers subdued the assailant, whose name has not been released, without firing a shot.
Instead, they stunned him with a Taser and took him into custody.
Authorities have spoken with him, as well as his family.
In a statement, London Mayor Sadiq Khan encouraged Londoners to “remain calm and vigilant” as the police presence in the city was heightened.
“As a precautionary measure, Londoners will wake up this morning to notice an increased presence on the streets of officers, including armed officers today,” Rowley said in a statement.