British Police fired a stun gun at a knife-wielding man as he ran towards officers guarding the Parliament on Friday.
Metropolitan police said they had not declared the incident as a terrorist incident since it was too early to understand the motivation. They said, however, that counter-terrorism officers would investigate the incident.
"At this time it is too early to understand the motivation so we have not declared this a terrorist incident," the Metropolitan Police said in a statement.
"However given the location, the circumstances and recent tragic events, the MPS Counter Terrorism Command will be investigating this incident."
"We remain open minded as to whether terrorism was a motive," the police added.