"A little more than 200 people have been rounded up in the raids nationwide on suspected madrassas (Islamic schools), offices of the militant outfits, shops and houses," an Interior Ministry official said on Wednesday.
Pakistan has been under pressure to act against fighters since it emerged that three bombers involved in the 7 July London attacks were British of Pakistani origin who had recently visited the South Asian country.
"The crackdown is in response to the London bombings," said a senior intelligence officer. "We are obviously under tremendous pressure to show the world that we are moving against militants."
A senior security official said President Pervez Musharraf had given "clear orders" to stamp out militancy and demanded a "zero tolerance" attitude against those spreading violence and hatred.
British Prime Minister Tony Blair on Tuesday said he was "anxious" for Pakistan to crack down on Islamic schools, while US Secretary of State Condoleezza Rice called Musharraf to discuss the "fight against terrorism," government officials said without elaborating.
Most of the arrests were made in the country's eastern Punjab province and in southern Sindh province, the Interior Ministry official said.
Police sources in Punjab said they had detained 65 suspected fighters from different cities, including 20 from Multan and about a dozen in the provincial capital Lahore.
Nearly 16 suspects were picked up in raids on at least four seminaries overnight in the capital Islamabad, where police used tear gas against hundreds of protesting students.
At least 52 people had been taken into custody during raids in hideouts, seminaries and houses in Sindh, said provincial home secretary Muhatarum, who has only one name.
"Reports I have received so far revealed arrests of 52 militants of outlawed groups, and more are likely to be arrested as we will not allow extremism at any cost," said Muhtarum, a retired brigadier.
Newspaper sellers were also
detained in Pakistan's crackdown
Thirty newspaper sellers were also detained within 24 hours for selling newspapers and magazines containing "hate material", said the Karachi president of the Newspaper Hawkers Association, Abdul Rahim Pathan.
Authorities in North West Frontier Province, bordering Afghanistan, said about 40 suspects had been detained in police raids in several cities.
"At least 40 suspects have been taken into custody, and the crackdown is in progress in all 24 districts of the province," provincial police spokesman Riaz Khan said.
Police in southwestern Baluchistan said they had arrested 30 suspected fighters during raids on seminaries and offices of religious groups in two districts of the province which also borders Afghanistan.