LONDON — A Norwegian teenager of Somali origin is suspected of going on a knife rampage through London’s tourist hub of Russell Square, ******* an American woman and injuring five other people, ****** said Thursday.

The London force sent extra officers into the city streets and mobilized counterterror detectives, but said the ************* suggested mental illness was the driving force behind the ******.

The ****** came just days after authorities warned the British public to be vigilant in light of ******* inspired by the Islamic State group elsewhere in Europe.

Metropolitan ****** Assistant Commissioner Mark Rowley said the ************* “increasingly points to this tragic ******** as having been triggered by mental-health issues.”

“So far we have found no evidence of radicalization or anything that would suggest the man in our custody was motivated by *********,” Rowley said.

The name of the **** woman, thought to be in her 60s, has not been released. Rowley said the five ******* people are British, American, Israeli and Australian, and none has life-threatening ********. Two remain in a hospital, while three others have been discharged.

Rowley said it appeared to be a “spontaneous ****** and that the ******* were selected at random.”

London Mayor Sadiq Khan urged the public to keep calm and remain vigilant.

“We all have a vital role to play as eyes and ears for our ****** and security services and in helping to ensure London is protected,” Khan said.

The Russell Square ******** came within hours of an announcement by London ****** that they were putting more ***** officers on the streets. The idea was to sustain public confidence following ******* by Islamic State-inspired groups in Europe.