ISLAMABAD Heavy gunfire and explosions rocked Islamabad early on Saturday as Islamist students holed up in a mosque battled Pakistani security forces after the militants' leader defied government demands to surrender.
The fortified Lal Masjid or Red Mosque compound has been under siege by hundreds of troops and police since Tuesday when months of tensions boiled over into clashes between Muslim clerics and religious students and security forces. At least 19 people have been killed.
"We can die but we will not surrender. We're not terrorists," said Abdul Rashid Ghazi, chief cleric leading the militants told Reuters early on Saturday, speaking over the crack of rifle fire.
Smoke and the orange glow of fire rose from the mosque early on Saturday as heavy gunfire and explosions rocked the city. It was not immediately clear what was burning.
Water, gas and power to the mosque have been cut and food was said to be getting scarce.
Tension between authorities and religious leaders at the mosque had been rising since January when students, most of whom in their 20s and 30s, launched a campaign to press for action against what they see as vice.
They kidnapped people they accused of involvement in prostitution, intimidated shopkeepers selling Western videos and abducted policemen and threatened to unleash suicide bombers if they were suppressed.
Moderate politicians and the media had urged President Pervez Musharraf to intervene to end the standoff. Musharraf has not commented publicly on the siege but has urged security agencies to allow time for parents to take children out of a madrasa, or school, in the compound.
"ASSASSINATION ATTEMPT"
On Friday, gunmen fired from a roof-top under the flight path from Islamabad's military airport as Musharraf was flying off to inspect flood damage in the south.
An intelligence officer, speaking on condition of anonymity, said the shots were an unsuccessful attempt on the president's life. But the government said there appeared to be no link between the shooting and Musharraf's flight.
U.S. ally Musharraf survived two assassination attempts by al Qaeda-linked militants in 2003.
Adding to a sense of foreboding over risks posed to stability by militants in nuclear-armed Pakistan, a suicide bomber killed six soldiers on Friday in a northwest region where the Islamists in the mosque have allies.
Many Pakistanis welcomed the government's move against a movement reminiscent of the Taliban in neighboring Afghanistan, and symptomatic of the religious extremism seeping into cities from tribal border areas.
Interior Ministry Secretary Syed Kamal Shah appealed to Ghazi to give up and said he would be treated humanely.
"There are many precious lives in his hands ... he should show courage and come out," Shah said. "If he is concerned about his safety, we are ready to give any guarantees."
But Ghazi said he and the followers were willing to lay down guns but would never accept arrest: "That's final, I can't change it."
He also said three student were killed on Friday but a paramilitary force commander denied that.
About 1,200 students have left the mosque since Tuesday but only a trickle of about 20 came out on Friday. Most were whisked away but one boy 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.
Authorities say they have blasted holes in the compound's walls to enable people to flee.
Ghazi rejected accusations he was keeping women and children as human shields.
Ghazi's elder brother and chief cleric, Abdul Aziz, was caught on Wednesday trying to flee disguised in a burqa. He later called on followers to give up. Aziz said there were 850 students inside, Ghazi said 1,900.
(Additional reporting by Faisal Aziz, Augustine Anthony, Zeeshan Haider)
Map of Pakistan showing Rawalpindi (near Islamabad).
During a flight Friday from Chaklala Airbase in Rawalpindi, Pakistan to Balochistan province, President Pervez Musharraf's plane was shot at from a rooftop near the flight path. Musharraf was flying to Balochistan province to observe the effects of recent flooding in the area.

The Pakistani government has officially denied the plane came under fire, but a Paksitani intelligence officer indicated, off the record, that an attempt of Mushaffaf's life had occurred. Musharraf's plane arrived safely at its destination. However, sources say that Intelligence agencies in Pakistan are investigating into possible connection between attack on the plane and the siege of Lal Masjid.

Police have cordoned off a house in Rawalpindi to investigate the incident. ''Reuters'' news agency had a photographer in the area at the time, and reported seeing two guns on the roof of the house, one of them an anti-aircraft gun, which had been mounted on the roof. The other gun was reported to be a machinegun. Deputy Inspector General of police Marwat Ali Shah confirmed that an anti-aircraft gun, a machine gun and ammunition had been recovered from the home. 

Local residents reported hearing the sound of gunfire. "Everyone heard a firing sound," Ishaq Ahmed told ''BBC News''. "The firing sound was like a bomb blast. It was that kind of sound." Some witnesses claimed that they saw a person along with a woman and two kids escaping on a motorbike after the incident.

General Musharraf has survived two previous attempts on his life, carried out on December 14, 2003 by al-Qaeda-linked militants. There is no indication or claim of responsibility, as yet, as to who carried out the latest attack.