Pakistan's president has issued an ultimatum to radical Islamists barricaded inside an Islamabad mosque.
President Pervez Musharraf told mosque leaders to free women and children and surrender "or they will be killed".
He spoke after troops outside the mosque stopped a delegation of Islamist politicians from entering to negotiate with those inside.
Hundreds of people are still inside the complex, which is surrounded by troops and armoured vehicles.
The delegates wanted to convince the mosque's leader, Abdul Rashid Ghazi, to allow women and children to leave.
Heavy bursts of gunfire and explosions rocked the Red Mosque overnight after armoured vehicles moved in and heavy exchanges of fire erupted at the complex early on Saturday.
Big chunks of debris, believed to be part of the mosque's perimeter wall, were blown high above the surrounding treetops.
Water and power to the mosque have been cut off and food is said to be getting scarce.
'Mass grave'
The BBC's Syed Shoiab Hasan, in Islamabad, says the area around the mosque is silent, except for the intermittent sound of gunfire and the boom of heavy weapons.
An increased military presence on the streets, combined with the refusal to let the political delegation through to the mosque, suggests that the government is now closing the door to negotiation, our correspondent adds.
In pictures: Siege scenes
Police have also seized control of a madrassa, or religious school, several kilometres away, which is also run by clerics from the mosque.
They described the Jamia Faridia as a "powerhouse" for the mosque and several of its students were involved in the stand-off.
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.
At least 19 people have been killed since the start of the stand-off.
Abdul Rashid Ghazi has said he and his followers are willing to lay down their guns but would rather die than surrender.
He told the BBC on Saturday that as many as 1,800 followers remain in the mosque, and claimed to have buried 30 female students in a mass grave in the compound
More than 1,000 supporters left earlier this week under mounting pressure from security forces.
About 60 of those remaining are said to be hard-liners 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.
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