Dozens of supporters of Imran Khan, the cricketer-turned politician, held a separate protest outside the court.

Court challenge

Both groups filed petitions to the court challenging the legality of Musharraf's eligibility to stand in the elections due to his dual role as civilian and military chief.

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The court is expected to rule early next week. Kamal Hyder, Al Jazeera's correspondent in Islamabad said although there was a heavy police deployment outside the court there were no "untoward incidents".

Larger opposition gatherings are expected to begin across Pakistan after Friday prayers.

Musharraf indicated on Tuesday that he would step down as head of the army if he is re-elected president, a move which would ostensibly restore civilian rule eight years after he took power.

Opposition parties say that for him to contest the election while remaining as head of the military would violate the constitution.

Musharraf reshuffled his senior military staff on Friday, appointing a new military intelligence chief.

Appointments 'monitored'

Nadeem Taj was director-general of the Inter-Services Intelligence (ISI), and promoted him from major-general to lieutenant-general.

Taj was formerly the head of military intelligence and also served as Musharraf's military secretary after he came to power in a bloodless coup eight years ago.

The move will increase expectations that the replaced ISI chief, Lieutenant-General Ashfaq Pervez Kiani, will get one of the top jobs - either replacing Musharraf as chief of army staff, or becoming his vice chief.

Al Jazeera correspondent Kamal Hyder said the new appointments will be closely monitored. "It will be interesting to see if this is a prelude to Musharraf announcing a successor before the election," he said.