Appearing on state-run TV, Maulana Abdul Aziz said about 850 students and children were inside the Lal Masjid or Red Mosque in Islamabad, two days after fierce gun battles with government forces in which at least 24 died. On Wednesday, some 1,200 students surrendered.
Aziz said among those barricaded inside were about 600 women and 14 men carrying submachine guns, the CNN report said.
Aziz reportedly was captured Wednesday after he tried to escape from the mosque, disguised in a traditional woman's burqa.
China's Xinhua news agency said Aziz in his appeal asked those inside to either surrender or escape.
Aziz also asked his brother Abdul Rashid Ghazi, the deputy of the mosque and seminary, to come out of the complex.
The CNN report said Pakistan forces, using loud speakers, had warned those inside that it was their last chance to surrender before a full-scale attack.
The students and their cleric leaders have occupied the mosque for months to press demands for imposition of strict Islamic laws in the city.
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