A man has been tasered outside the Palace of Westminster in London after he allegedly reached for a knife when approached by officers.
Police became aware of the suspect, aged in his 30s, acting suspiciously, Scotland Yard said.
The Metropolitan Police then discharged a Taser after the man allegedly reached for a knife.
No one was injured in the incident.
Westminster pic.twitter.com/S8gsZqhx7N— Kate Proctor (@Kate_M_Proctor) June 16, 2017
The bearded suspect, wearing black trousers and a grey sweatshirt, was led away into a van by officers after being detained for around 30 minutes outside the Houses of Parliament.
He remains in custody at a central London police station, the force added.
He was held with his arms against his back just yards from the forecourt of the building, where Pc Keith Palmer was stabbed to death by terrorist Khalid Masood in March.
A review of security at the perimeter of the parliamentary estate was ordered by Commons Speaker John Bercow following the incident.
The use of armed officers and physical barriers has become more visible, while a permanent barrier has been erected to protect pedestrians on Westminster Bridge, where Masood murdered four people and injured more than 50 others by mounting the pavement in a car.
Bradley Allen, 19, from Barking, east London, said he saw the man with clenched fists moments before he was detained.
Mr Allen said he was walking past Parliament when he saw a "dark male stood there, who looked quite angry with fists quite clenched".
"He stared at me and my mate and we walked past him. Within seconds there was a shout and police ran out of the front gate shouting at him 'Get on the floor, get on the ground'.
"Within seconds he was on the ground - I'm not sure whether he was Tasered - I'm not sure how he got down there, but in seconds it was over.
"Armed police everywhere, telling everyone to move back, and we all got pushed back."