Four soldiers were killed in a bomb attack in Pakistan's North West Frontier province in an apparent retaliation to the crackdown on radical clerics and students of a mosque in Islamabad.

The attack was carried out in the town of Chakdara in Dir district, the conservative area in the province.

No group claimed responsibility for the attack, but the bombing is believed to be linked with the military operation against the Lal Masjid in Islamabad.

TV channels reported that an army convoy was heading to Mingora, a main city in the region, when a cycle bomb was exploded by remote control. Two army officers are among those who died. One soldier was injured in the attack.

The convoy consisting of some 50 vehicles was heading to Mingora, where thousands of people were staging a rally in support of the clerics of Lal Masjid, to prevent any untoward incident, reports said.

Maulana Fazal Mulla, the leader of a banned group, had reportedly threatened to attack government buildings in the area if the operation against Islamabad's mosque was not stopped.

The Imam of Lal Masjid Maulana Abdul Aziz had threatened in his speeches before his arrest that his followers will resort to suicide attacks if operation was launched against his mosque.