ISLAMABAD, Pakistan (CNN) -- Pakistani forces early Thursday demolished the front walls of a radical mosque, where battles between security forces and students have raged for two days, intelligence and military sources told CNN.
Radical students sit in a holding area Wednesday after surrendering.
By loudspeaker, the forces warned students inside the Lal Masjid, or Red Mosque, that they had one last chance to surrender before a full attack took place.
More than 1,200 of the students have already surrendered, but hundreds more remain inside.
Heavy gunfire from both sides, punctuated by loud explosions and the firing of tear gas, erupted shortly before 4 a.m. Thursday (7 p.m. Wednesday ET).
The attack came hours after the mosque's top cleric was arrested while trying to slip away wearing a traditional woman's burqa.
At least 24 people, including two members of the security forces and one journalist, have been killed in the two days of battles.
Tensions have been simmering between police and students at the mosque, who are blamed for a string of recent kidnappings of civilians, Chinese nationals and Pakistani police. The government has been investigating the activities of the mosque, whose students are demanding sharia, or Islamic law, be instituted in Islamabad.
As part of the clampdown on the mosque compound -- which includes several madrassas, or religious schools -- police set up a security perimeter last week.
The violence began Tuesday when about 150 militant students attacked a police checkpoint close to the mosque. Police fired tear gas and the students fought back with sticks and guns.
More than 1,200 of the students surrendered, but hundreds more remained inside. Pakistan President Pervez Musharraf earlier announced he would give 5,000 rupees ($83) to any student who surrendered.
Brigadier Gen. Tareen of the Pakistan Rangers, head of the military operation at the mosque, said the older students inside were using young boys and girls as human shields.
"We will establish writ of the government at any cost and these people don't have any other choice other than to surrender," he said.
The Pakistan Rangers, a paramilitary group, are conducting the operation with the help of Pakistani police and army. The area around the mosque has been totally sealed, and nobody is allowed to enter or leave. E-mail to a friend
CNN's Syed Mohsin Naqvi contributed to this report.