Islamabad (PTI): At least 20 people were killed and about 50 injured when a suicide bomber blew himself up inside a hospital in a town in Pakistan's troubled northwest on Tuesday.

Local officials in Dera Ismail Khan in North West Frontier Province told TV channels that the suicide bomber detonated his explosives near the emergency ward in the district hospital in the city.

Police officials said they have found the head and parts of the body of the suicide bomber.

Some reports said the explosion took place as Shiite Muslims gathered to protest the death of a man from the community in a suspected sectarian attack. The man was earlier brought to the emergency ward of the hospital.

A senior police official and other security personnel were among the injured. Officials said they feared the toll could rise as several of the injured were in a serious condition.

The attack sparked panic in the local market and traders shut down their shops. Police advised people to return home and stay indoors.

The blast came amid an ongoing military offensive in the nearby Bajaur tribal region that has left hundreds dead and triggered threats of retaliation from the local Taliban.