London police arrested a man for possession of weapons Thursday near Britain's Houses of Parliament.
The Metropolitan Police force said no one was injured in the incident, which brought armed police flooding into the area around Parliament.
Witnesses reported seeing armed police blocking off Whitehall, a street lined with government buildings, and a man on the ground surrounded by police.
A black-clad man could later be seen standing on the sidewalk, surrounded by police, before being put into a police vehicle.
A photo showed a forensic officer looking at a black bag and what appeared to be two knives on the ground.
Security has been increased around Parliament after an attacker drove an SUV into pedestrians on nearby Westminster Bridge on March 22, killing four, before stabbing a police officer to death inside the gates of Parliament. The attacker, Khalid Masood, was shot dead by police.
Police believe Masood, 52, a British-born with convictions for violence, acted alone.
Thursday is Parliament's last sitting day before Britain's June 8 election.
Police say there has been a surge in knife crimes in London in the past year.
Britain also faces a threat from international terrorism classified as "severe," meaning an attack is highly likely.