Azeem said: "The time for rhetoric is over. He must come out with the women and children he is using as shields, hand over all the weapons, and bring it to a decent closure."
Witnesses have reported hearing explosions in the area.
Aftab Khan Sherpao, the country's interior minister, said troops were trying to blast holes in the walls of the fortress-like compound of the mosque, also known as Lal Masjid, and an adjoining seminary for girls.
Rageh Omaar, Al Jazeera's correspondent in Islamabad, said: "There are ambulances arriving. There are reports Abdul Rashid Ghazi is going to give himself up."
He said a huge number of Pakistani troops were massing together.
Burqa escape bid
Earlier, Abdul Aziz Ghazi, who is Abdul Rashid's brother and the captured leader of the mosque, had called on his followers still inside the complex to surrender or flee.
Dozens of students from the mosque and its religious school had surrendered on Thursday.
Abdul Aziz was arrested by security forces on Wednesday night after trying to escape the compound in a burqa, a long enveloping garment worn by Muslim women.
In an interview broadcast on state television on Thursday, he said about 850 students remained inside, including 600 women and girls, and 14 men who were armed with Kalashnikovs.
Abdul Aziz, who was in a burqa, said people still inside would not be able to hold out for long.
Smiling through much of the interview, he said he left the mosque to stop the bloodshed, and had urged others to do the same, but some women teachers had persuaded girls to stay behind.
Ready for talks
Earlier on Thursday, speaking to Al Jazeera's correspondent, Abdul Rashid said that about 2,000 students remained inside and said the conflict did not need to end in bloodshed.
Abdul Rashid had said on Wednesday that he was prepared to talk with the government, but added: "We will continue to defend ourselves".
He said the mosque had enough supplies to carry on "until God wants".
The siege began when the Pakistani army surrounded the mosque on Wednesday, a day after at least 16 people were killed in clashes between security forces and armed activists from the mosque.
Liberal politicians had been pressing Pervez Musharraf, Pakistan's president, for months to crack down on the brothers running the Red Mosque.
|The students carried out provocative acts |
over the past six months [AFP]
Musharraf himself has accused the mosque of sheltering al-Qaeda members.
The students carried out a series of provocative acts over the past six months, demanding the enforcement of Islamic law, and running a vigilante anti-vice campaign.
Abdul Aziz had also threatened suicide attacks if force was used against his movement.
About 1,200 students walked out of the mosque compound on Wednesday in exchange for a pardon and a payment of $83 (5,000 rupees).
Tariq Azim, the deputy information minister, had said that all women and children would be granted amnesty, but men involved in killings and other crimes as well as mosque leaders would face legal action.