At least nine persons, including four security personnel, were killed and several injured in a suspected suicide attack on an army convoy in the restive Swat valley in northwestern Pakistan on Sunday.

The convoy was attacked near Mingora, the headquarters of Swat district, eyewitnesses said.

The blast damaged a petrol pump, several shops and some cars. A witness said the convoy was apparently hit by a suicide bomber who was in a jeep.

The attack caused widespread panic in Mingora and curfew was re-imposed across Swat valley. The attack came hours after security forces launched a drive against militants in the Gulibagh, Balalai and Waliabad areas of Swat.

After clearing these areas of militants, security forces established new check posts.

Nearly 300 militants have been killed in Swat since the army launched a major operation against armed followers of pro-Taliban cleric Maulana Fazlullah in mid-November. Over 150 rebels have also been captured though the security forces are yet to trace Fazlullah, who is on the run.

Fazlullah, known as 'Mullah Radio' for his sermons advocating jihad broadcast from an illegal FM station, has been heading a campaign for enforcing Shariat or Islamic law in Swat, located just 160 km from Islamabad.