The suspect was known to British security agencies and was thought to have been inspired by the Islamic State group. Authorities haven’t released the man’s name. Police said knives were recovered during the operation and that there was “no immediate known threat” to the public. The man was being held at a London police station on suspicion of possession of an offensive weapon and on suspicion of the commission, preparation and instigation of acts of terrorism. Whitehall, a street lined with government buildings that is the main artery of London’s government district, was blocked during operation. Security has been increased around Parliament after an attacker drove an SUV into pedestrians on nearby Westminster Bridge on March 22.