Islamist militants fighting the government of nuclear-armed Pakistan have launched a string of bomb attacks in Peshawar, which is the gateway to Afghanistan, killing hundreds of people over the past year.

The latest blast went off in an area of the old city known as the Storytellers' Bazaar as a protest against power cuts organized by a religious party was breaking up, officials said.

Several officials of the Jamaat-i-Islami (JI) party, which organized the protest, were among the dead, said members of the party which has a record of sympathizing with Islamists.

Police officer Imran Kishwar said 23 people had been killed and 29 wounded.

It was the second blast in the city on Monday.

Earlier, a six-year-old school boy was killed and five boys and two other people were wounded when explosives went off outside their school in the city, doctors said.

Security forces have made significant gains against the militants in offensives over the past year, clearing the fighters from strongholds in the Swat valley and in the regions of South Waziristan and Bajaur on the Afghan border.