At least 335 religious students, mostly women, were killed in an overnight operation launched by the Pakistan army at the besieged Lal Masjid in Islamabad, Abdul Rashid Ghazi, cleric of the controversial mosque, claimed on Sunday.
Rashid said that 310 female and 25 male students were killed in bombing of the compound of the mosque, TV channel reported.
There was no official confirmation of Rashid's claim.
The bombing was expected to blow up sections of the walls and make holes in the compound so that the students who had been taken hostages could escape, an army spokesman said.
The five-day heaviest firing and explosions continued late on Saturday night and the security forces made advancement towards Lal Masjid, Jamia Hafsa.
15 armoured vehicles advanced from the rear side of the building and opened fire, as the electricity of the nearby areas was cut off.