At least 38 people were killed and over 50 injured in a suicide attack during the funeral prayers of a police officer, slain by militants, in northwestern Pakistan on Friday.

The bomber blew himself up today evening in the midst of a large number of people attending the funeral prayers for Deputy Superintendent of Police Javed Iqbal Mastikhel, who was killed with three of his guards in a roadside bomb attack in the morning.

"It was a suicide attack," said Interior Ministry spokesman Javed Iqbal Cheema.

The blast occurred as a police contingent was presenting a guard of honour to the slain police officer on the lawns of a school at Mingora, the main town of Swat district in the North West Frontier Province. Most of those killed and injured were policemen. Among the dead were Mingora's Station House Officer Habib Zaman, Mastikhel's son and a former provincial assembly member, officials said.

The injured, many of them in a critical condition, were rushed to the state-run hospital in Saidu Sharif town. Officials said they feared that the toll could rise.

Curfew was imposed across Swat following the suicide bombing, the latest in a series of such attacks on security forces in northwestern Pakistan. The security forces are conducting a major operation in Swat against militant followers of radical cleric Maulana Fazlullah.

Mastikhel and his guards were killed when the van they were traveling in was targeted with a roadside bomb near the officer's home at Lakki Marwat town in the North Western Frontier Province. Two other policemen were injured in that attack.

In a separate incident, an army convoy was targeted with a roadside bomb at Badhaber in Peshawar, the capital of the NWFP, though only a civilian was injured in the blast, police said.

No group has claimed responsibility for the three bombings though such attacks are usually blamed on pro-Taliban militants active in the NWFP and the tribal areas bordering Afghanistan.