Islamabad: Security forces clashed with militants outside a radical mosque where students have carried out a string of kidnappings of police officers and alleged prostitutes, killing at least five people, officials said.

The battle on Tuesday marked a major escalation in a standoff at the Lal Masjid, or Red Mosque, whose clerics have challenged the government by mounting a vigilante anti-vice campaign in the Pakistani capital of Islamabad.

Doctors at two hospitals said the five dead included two policemen, one soldier, a militant and a civilian. However, clerics at the mosque claimed that 10 of their supporters died, according to a lawmaker sent to mediate.

The trouble began when student followers of the mosque, including young men with guns and dozens of women wearing black burqas, rushed toward a nearby police checkpoint. Police and paramilitary soldiers fired tear gas and, as the students retreated, some of them masked, fire shots toward security forces.

Gunfire was also heard from the police position.

The mosque has long been a flashpoint in the capital with authorities locked in a tense stand-off with the student movement, who seek to impose Taliban like social values in the city.

The students used the mosque loud speakers to appeal to residents to support them.

The students later pelted two government buildings, including the Ministry of Environment, with rocks and set them ablaze, and torched a dozen cars in the ministry's lot.

Hours after the clashes, dozens of students were patrolling the area around the mosque, some carrying gas masks, gasoline-filled bottles and Molotov cocktails. About a dozen were armed with guns, including AK-47 assault rifles.

Security forces cordoned off the area with barbed wire and checkpoints and continued to fire tear gas at demonstrators from a distance. Shops in the area were shuttered.