British police did not rule out the possibility of “terrorism” after the attacker was put under arrest following the incident in Russell Square in the center of the British capital on Wednesday.

Up to six people have also been injured, according to the Metropolitan Police.

“Terrorism is one possibility being explored at this stage,” police said in a statement. “A female (no further details) was treated at the scene but was pronounced dead a short time later. We await an update on the condition of the other persons injured and details of any other injuries.”

The suspect, who was said to be in possession of a knife, “was arrested at 22:39 hours and a Taser was discharged by one of the arresting officers. Additional police units have been deployed to the area to provide reassurance.”

Police said early on Thursday that mental health was a main factor in the attack.

"Early indications suggest that mental health is a significant factor in this case and that is one major line of inquiry," Mark Rowley, the Met assistant commissioner, told reporters.

The attack was reported at a time when Europe remained on edge over fear of terror attacks by ISIS terrorists across the continent, Press TV reported.

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