The Jamia Hafsa was accused of links to the 7/7 London bombings

The women, from the nearby Jamia Hafsa madrassa, burst in late on Tuesday, demanding the premises be shut down.

The women say they have a right to end immoral activity under Islamic law.

The BBC's Navdip Dhariwal in Islamabad says it is the first time such bold Taleban-style activity seen elsewhere in Pakistan has occurred in the city.

The Jamia Hafsa school has been at the centre of controversy in recent months.

In February, armed students prevented the authorities from demolishing an illegally constructed mosque and occupied a nearby children's library.

They have also demanded that local video owners close their stores.

'Not mistreated'

Correspondents say prostitution is widespread in Pakistan, even though it is illegal.

The women who led Tuesday night's raid near the city centre included teachers and students incensed, the school says, by reports the house was being used for immoral purposes.

They [police] have arrested our respected, veiled teachers for a corrupt woman

Abdul Rashid Ghazi,

Jamia Hafsa vice-principal

Profile: The red madrassa Inside the Jamia Hafsa

They were later joined by male colleagues from the men's section of the madrassa.

When the alleged brothel's owner refused to shut the building, the raiding party forcibly shut it themselves and took the woman, her daughter and daughter-in-law back to the madrassa where they are still being held.

Initially the police were reluctant to step in to rescue the woman, but later registered a case and arrested two female teachers of the school.

But students then kidnapped two policemen from a nearby patrol. They too are being held in the madrassa and were allowed to speak to reporters.

"They have not mistreated us, they have served us tea and allowed us to keep our mobile phones," one of them, constable Hamad Raza said, the AFP news agency reports.

"We are told that negotiations are under way and we hope the matter will be over soon," he said.

School officials also say that two other teachers have been missing since early on Wednesday morning and that they believe they were kidnapped by intelligence agencies.

Their whereabouts is unclear.

School raided

The Jamia Hafsa has long been a problem for the capital city administration and Pakistan's President General Musharraf.

It has often criticised his policies in the "war on terror" and called for Islamic law to be enforced in Pakistan.

The madrassa was among schools raided after the London bombings of July 2005 over alleged links with the bombers.

Madrassa officials deny any such links.

Our correspondent says it appears the administration is reluctant or helpless to take action against the school's teachers and students.

The incident comes amid concerns over the increasing "Talebanisation" of parts of Pakistan.

In Pakistan's tribal areas and in North West Frontier Province (NWFP), religious groups have sought to impose strict Islamic law on local people.

Across the tribal areas and in parts of NWFP, video and CD shops have been attacked and closed, barbers are banned from shaving beards and non-religious music and singing is prohibited.