The UK police have found no evidence of radicalization or terror motives behind Wednesday’s stabbing spree in London that killed one woman and injured five others.

The attacker, a 19-year-old Norwegian man of Somali origin, was arrested by police on suspicion of terror links, but those possibilities were rejected after police interviewed him and his family.

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

“While the investigation is not yet complete, all of the work that we have done so far increasingly points to this tragic incident as having been triggered by mental health issues.”

According to police, an American woman, who was in her 60s, was killed in attack while two other women and three men were injured by the suspect.

Rowely said the attack was “spontaneous” and all victims were randomly targeted by the knife-wielding assailant.

The official said British intelligence services were working with police to get a full picture of the attacker. Some locations in North and South London were also being inspected, he added.

Police Commissioner Bernard Hogan-Howe confirmed that the number of armed police officers patrolling the streets of the capital has dramatically increased.

The attack came amid growing warnings by British security officials about an imminent terror attack in the country.

Just before the attack happened on Wednesday, London police announced a plan to deploy an additional 600 armed officers across the city to protect against possible terror attacks.

The decision was made in light of the recent terrorist attacks across Europe including those in France.

"Anyone who's been following events in Europe over the past few weeks will understand why we want to show our determination to protect the public," Hogan-Howe said at the time.

London was last hit by a terror attack on July 7, 2005, when four extremists targeted three underground trains and one bus, killing 52 people.

However, the threat level there remains at "severe" now following two terror attacks in France and similar ones in Germany.