Pakistan's religious affairs minister has said radical Islamists are holding women and children hostage inside a besieged mosque complex in Islamabad.
Troops are blocking all entrances and roads to the mosque
Ejaz-ul-Haq told the BBC those in control of the Lal Masjid, or Red Mosque, were "hardened terrorists".
Pakistani Prime Minister Shaukat Aziz said he suspected some of the combatants were trained militants.
At least 21 people have died since fighting erupted when the army surrounded the mosque last week.
An army commander was shot dead by gunmen inside the mosque on Sunday.
The mosque's leader, Abdul Rashid Ghazi, has said he and his followers would commit suicide rather than surrender.
Abdul Rashid Ghazi said as many as 1,800 followers remained in the mosque, although this cannot be verified.
Mr ul-Haq said women and children have been locked up on two floors of the Jamia Hafsa religious school, which is attached to the mosque.
"The situation still is that the control of Jamia Hafsa and Red Mosque is now in the hands of the militants who were taken in by the brothers to guard them," he said.
The minister added that there were "as many as five hardcore terrorists inside the mosque".
Mr ul-Haq said a combatant killed on the first day of the siege was identified as Maqsood Ahmed, a member of Jaish-e-Mohammad, an outlawed radical Muslim organisation which has been linked to al-Qaeda.
Ahmed was wanted in connection with an assassination attempt against Mr Aziz in the northern Pakistani town of Attock in 2004.
Mr Aziz said the identity of the combatants inside the mosque was unclear.
But he said there seemed to be trained militants "and whenever they come out, we will know who they are and if they are wanted criminals".
Abdul Rashid Ghazi has denied the presence of any banned extremist groups.
He says those inside are students of his religious school and he is in charge.
Earlier, Mr ul-Haq said up to 250 militants - including foreign radicals - were leading the fighting.
'Surrender or die'
The commander, Lt Col Haroon Islam, was shot dead during an operation to blow holes in the mosque compound walls to enable civilians to escape.
Water and power to the mosque have been cut off and food is said to be getting scarce.
The BBC's Shoaib Hasan in Islamabad says he has heard intermittent gunfire in the area and the boom of heavy weapons.
Col Islam was shot dead by students inside the mosque
An increased military presence on the streets, combined with the refusal to let a delegation of Islamic figures through to the mosque, suggests that the government is now closing the door to negotiation, our correspondent says.
On Saturday, Pakistani 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.
More than 1,000 supporters left last week under mounting pressure from security forces, although only about 20 have left since Friday.