British police said officers guarding one of the gates to the Westminster parliament in central London had fired a stun gun at a man who reached for a knife when they approached him on Friday but it was not initially being considered a terrorist incident.
London police (MPS) said the man was acting suspiciously at around 11 a.m. (6.00 a.m. ET) near one of the gates where a militant killed a policeman less than three months ago.
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."
A witness at the scene told Reuters the man, who police said was in his 30s, had run towards one of the gates.
"You could tell he was suspicious, he was stood there fists clenched. He looked quite an angry geezer," Bradley Allen, 19, told Reuters.
"We got seconds down the road and they had him on the floor, pinned. Police around him, telling everyone to move back."