Police swooped on Islamist and other opposition activists ahead of protests on Friday against the sacking of Pakistan's top judge, arresting nearly 100 people, police and party workers said.
Around 30 people, including several hardline MPs, were arrested in the capital Islamabad in overnight raids, a senior police officer told the agency on condition of anonymity.
Police in the eastern city of Lahore detained more than 50 opposition activists, mainly workers from the fundamentalist Jamaat-e-Islami party, a top city police official said.
"I have been detained by the police and they have brought me back to my home," said Liaqat Baluch, a senior leader of Pakistan's main alliance of Islamic parties, the Muttahida Majlis-e-Amal (MMA) or United Action Front.
"They said that I cannot lead the rally in Lahore."
At least a dozen people were also arrested in the town of Taxila near Islamabad, while in the central city of Faisalabad a former MP from the Pakistan People's Party of former premier Benazir Bhutto was held, police said.
"Several of our MPs and workers have been arrested in Islamabad and Rawalpindi (adjoining the capital), also in Lahore," MMA spokesman Shahid Hamsi said.
"The government wants to prevent us from holding the demonstration but we will go ahead with our march."
Military ruler President Pervez Musharraf suspended chief justice Iftikhar Muhammad Chaudhry a week ago on charges of misconduct and abuse of power.
Chaudhry was due to appear later Friday for a second time in four days before a judicial accountability council at the Supreme Court, which is ruling on the case.