British police said counter-terrorism officers would investigate a knife-wielding man arrested outside Parliament, although they had not declared it as a terrorist incident.
Armed police fired a stun gun at a man who reached for a knife as he ran towards officers guarding one of the gates to the Westminster parliament in central London on Friday, witnesses said.
"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."
Police said the man was acting suspiciously at around 11:00am (local time) 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. He has been taken to a central London police station, where he remains in custody.
Armed police had guns trained on the man as he was restrained and bundled into a police van, witnesses at the scene said.
A witness at the scene told reporters 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 local media.
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