Pakistani religious students (in black) meet with their mother (2nd L) after surrendering outside the Lal Masjid, or Red Mosque, in Islamabad July 5, 2007. [Reuters]

Earlier, gunmen fired at Pakistani President Pervez Musharraf's plane as it took off from Islamabad's military airport, an intelligence officer said.

The government confirmed shots had been fired from a roof near the airport but said there appeared to be no link to the president's flight to inspect flood damage in the south.

Adding to a sense of foreboding over risks posed to Pakistan's stability by Islamist militants, a suicide bomber killed six soldiers in a northwest region where the hardliners in the Islamabad mosque have allies.

Musharraf has not commented publicly on the siege at Islamabad's Red Mosque, or Lal Masjid, but has urged security agencies to be patient and allow maximum time for parents to take children out of a madrasa, or school, in the mosque compound.

At least 19 people have been killed in clashes that erupted outside the mosque on Tuesday and the compound has been under siege by hundreds of troops and police.

Water, gas and electricity supplies have been cut and food was running out, said a boy, one of about 20 people who left the fortified compound on Friday.

Nearly an hour of intense fire erupted at around 6 p.m. (1300 GMT). Two loud blasts, which a television news channel said came from students firing rocket-propelled grenades, shook the leafy neighborhood that has been under curfew since Tuesday.

"ASSASSINATION ATTEMPT"

Regarding the Musharraf plane incident earlier, an intelligence officer, speaking on condition of anonymity, said the shots fired from a house close to Islamabad's military airport had been an unsuccessful attempt on the president's life.

"There was an attempt, that was missed," said the officer.

U.S. ally Musharraf, who came to power in a military coup in 1999, survived two assassination attempts by al Qaeda-linked militants in December 2003.

A Reuters photographer saw two machineguns mounted between satellite dishes on the flat roof. The Interior Ministry said two anti-aircraft guns had been found but had not been fired. It said a 7.62 mm sub-machinegun that was also found had been fired.

"There does not appear to be any linkage between the incident and the president's flight," it said.

The cleric inside the Lal Masjid, Abdul Rashid Ghazi, has said he and the followers of his Taliban-style movement were willing to surrender but he also set conditions, including safe passage.

The government rejected his demands and insisted he release women and children it says he is holding as human shields, and surrender unconditionally.

But Ghazi told Geo TV he would not bow to pressure: "We can be martyred, but we will not court arrest."

A boy who surrendered after sneaking out of the mosque said older students were forcing younger ones to stay. Food was running out and the stench from dead bodies hung in the air, Ashraf Swati, 15, told Reuters.

Militants later fired on other some parents approaching the mosque in the hope of collecting their children, wounding one.

Tension between authorities and the mosque had been rising since January when the students, most of whom are in their 20s and 30s, launched an increasingly provocative campaign to press for various demands including action against vice.

They threatened suicide attacks if suppressed.

There was no indication a suicide bomber who killed six soldiers in the northwest was acting in support of the mosque radicals, but it is known to have supporters in the region.

Ghazi's elder brother and chief mosque cleric, Abdul Aziz, was caught on Wednesday trying to flee disguised in a woman's all-covering burqa. He later called on followers to give up.

About 1,200 students have come out. Aziz said there were some 850 students inside while Ghazi put the number at 1,900.

Many Pakistanis welcomed the action against a movement reminiscent of the Taliban in Afghanistan, and symptomatic of the religious extremism seeping into cities from tribal border areas.

Moderate politicians and the media had urged Musharraf to act sooner but he cited concern about bloodshed.