Armed police fired a stun gun as they detained a knife-wielding man outside the British parliament.
Police say the man reached for a knife as he ran towards officers guarding one of the gates to the Houses of Parliament in central London.
After firing a Taser stun gun, police detained the man. Armed police had guns trained on the suspect as he was restrained and bundled into a police van, witnesses at the scene told Reuters.
"The man reached for a knife," police said in a statement. "At this time it is too early to understand the motivation so we have not declared this a terrorist incident. However given the location, the circumstances and recent tragic events, the MPS Counter Terrorism Command will be investigating this incident."
The incident occurred less than three months since a man drove a car into pedestrians on Westminster Bridge, killing four, and then stabbed a policeman to death in the grounds of parliament. He was shot dead at the scene.
That attack was followed by a suicide bombing at a pop concert in Manchester which killed 22 and a similar deadly attack on London Bridge earlier this month, thrusting security and policing to the fore of campaigning before last Thursday's election.
Scotland Yard said the man - aged in his 30s - was arrested on suspicion of possessing a knife.
- Reuters / BBC