PESHAWAR, Pakistan: A bomb blast inside a Sunni Muslim mosque on Saturday killed five people and wounded 28 others in Pakistan's northwestern city of Peshawar, officials said.

The explosion took place while people were saying afternoon prayers in the mosque located in the densely populated Mohalla Baqar Shah area of Peshawar city.

"The death toll rose to five after a blast victim died of his wounds in hospital," local senior police official Khalid Hamdani told AFP.

Earlier another local police official, Imran Shahid, said the bomb was planted inside the mosque.

He said there were up to 40 people in the building at the time of the blast.

Prime Minister Raja Pervez Ashraf condemned the bombing and said "such acts of terror cannot weaken the nation's resolve to wipe out terrorism from our society", an official statement said.

Peshawar is vulnerable to bomb blasts and Taliban attacks as it runs into the semi-autonomous tribal belt, considered a safe haven for Taliban, Al-Qaeda and other insurgents fighting both in Pakistan and across the border in Afghanistan.

The attack comes six days after a car bomb killed 50 people in a mainly Shiite Muslim neighbourhood of Karachi, the fourth in a series of major attacks on the minority Shiite community since January 10 that have killed more than 250 people.

Pakistan's parliament is due to dissolve in less than two weeks in preparation for elections, but rising sectarian violence has raised serious questions about security.

Pakistan says 35,000 people have been killed as a result of terrorism since the 9/11 attacks and the 2001 US-led invasion of Afghanistan.