Pakistani officials say the latest crackdown has resulted in the arrest of up to 600 suspected militants, clerics and Islamist activists across the country.
Those detained include members of outlawed militant organizations, clerics accused of delivering "provocative" speeches, and Islamists accused of publishing or distributing hate material. At least 295 of the detainees belong to militant groups outlawed over the past three years.
President Pervez Musharraf ordered the crackdown after revelations that some of the suspected suicide bombers in the July 7 attacks on London were Britons of Pakistani descent who had visited Pakistan. But Pakistani officials say the arrests had nothing to do with the London bombings.
The officials say some of those detained will be tried under Pakistan's anti-terrorism law, which allows authorities to hold a suspect up to a year without laying charges.