Pakistani police have stepped up their operations at a mosque in Islamabad, on the fifth day of confrontation with radical Islamists barricaded there.
Heavy bursts of gunfire and explosions rocked the Red Mosque overnight after armoured vehicles moved in.
Police also seized control of a seminary several kilometres away, which is run by clerics from the mosque.
Several hundred people, including children, have been inside the mosque holding out against the authorities.
Water and power to the mosque have been cut off and food is said to be getting scarce.
Heavy exchanges of fire erupted at the complex early on Saturday.
In pictures: Siege scenes
The two explosions overnight were the biggest so far in the siege and were heard as far as 8km (5 miles) away.
Big chunks of debris, believed to be part of the mosque's perimeter wall, were blown high above the surrounding treetops.
On Friday an attempt by a group of students to break out sparked a co-ordinated assault on three sides by armoured personnel carriers and rangers.
Two students were killed and at least 10 wounded, four of them seriously.
At least 19 people have been killed since the start of the stand-off.
The mosque's deputy leader, Abdul Rashid Ghazi, said he and his followers are willing to lay down their guns but would rather die than surrender.
"We are ready for our heads to be cut off but we will not bow to the authorities," he said.
Madrassa captured
Meanwhile Pakistani police have taken control of an Islamic seminary run by clerics from the Red Mosque.
"Police stormed into Jamia Faridia (school) and arrested dozens of students and shifted them to an unknown place", a senior security officer told AFP news agency.
Police say the school was a "powerhouse" for the mosque and several of its students were involved in the stand-off.
It is believed several hundred religious students are still inside the Red Mosque complex, after more than 1,000 left under mounting pressure from security forces.
Officials said about 60 of those remaining are hard-liners, who have been at the vanguard of campaigning for the imposition of strict Islamic law (Sharia) in Islamabad.
They have led a morality campaign which included the abduction of police officers and people accused of running brothels, as well as raids on music and DVD shops.
The BBC's Barbara Plett in Islamabad says the government is piling psychological pressure on those still inside with a mass demonstration of force demanding unconditional surrender.
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