Those detained include members of the Pakistan Muslim League-Nawaz (PML-N), which is headed by Nawaz Sharif, a former prime minister who last month was disqualified from running in elections.

Anti-government lawyers and opposition parties are expected to launch a cross-country protest rally from Punjab to the capital Islamabad, known as the long march, on Thursday.

The parties are calling for the reinstatement of Iftikhar Chaudhry, a former supreme court justice, and other judges dismissed by Pervez Musharraf, Pakistan's former president.

Protest ban

Pakistani authorities announced a ban on rallies and protests throughout Punjab province before the march.

"It has been done to maintain law and order," Farhan Aziz Khawaja, a senior provincial official, told the Reuters news agency.

"From now on, there's a ban on all sorts of processions, protests and congregations for one month."

But opposition leaders said the ban will not affect their plans.

"We will remain peaceful and will peacefully defy the ban on the long march," said Siddiq-ul-Farooq, a spokesman for the PML-N.

Supporters of the PML-N have been protesting daily in Punjab against a supreme court order banning Sharif and his brother from standing for election.

The provincial government, which was led by Sharif's party, has been dismissed by Asif Ali Zardari, Pakistan's president, and federal rule imposed.