A Pakistani colonel has been killed in the latest clashes with Islamist students barricaded inside a mosque in the capital, Islamabad.
Troops are blocking all entrances and roads to the mosque
The army said the commando officer had been overseeing an operation to blast holes in the walls of the Red Mosque when he was shot by students.
Troops were carrying out the attack in an attempt to allow women and children trapped inside the mosque to escape.
About 20 people have now been killed since the stand-off began last Tuesday.
Another soldier was wounded in the latest clashes. Both men belonged to the army's Special Services Group.
On Saturday, President Pervez Musharraf told the students they had no option but to surrender.
"We have been patient. I want to say to the ones who have been left inside: they should come out and surrender, and if they don't, I am saying this here and now: they will be killed," he said.
He was speaking after troops outside the mosque stopped a delegation of Islamic figures from entering to negotiate with those in the complex.
The delegates wanted to convince the mosque's leader, Abdul Rashid Ghazi, to allow women and children to leave.
Water and power to the mosque have been cut off and food is said to be getting scarce.
The BBC's Syed Shoiab Hasan, in Islamabad, says he has heard intermittent gunfire in the area 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.
On Saturday police also seized control of a madrassa, or religious school, several kilometres away, which is also run by clerics from the mosque.
Police described the Jamia Faridia school as a "powerhouse" for the mosque and said several of its students were involved in 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, though neither claim can be verified.
More than 1,000 supporters left earlier this week under mounting pressure from security forces.
About 60 of those remaining are said to be hardliners campaigning for the imposition of strict Islamic law (Sharia) in Islamabad.
They have led a morality campaign which in recent weeks included the abduction of police officers and people accused of running brothels, as well as raids on music and DVD shops.