A suicide bomber targeted a Shiite Muslim mosque in northwest Pakistan on Friday, killing 24 people and wounding up to 55 as worshippers poured out of weekly prayers, officials said.

The bomber detonated explosives packed into a motorcycle in a narrow lane containing both the Shiite and a Sunni Muslim mosque in the town of Hangu, the latest bloody sectarian attack in a country where such violence is on the rise.

Pools of blood and pieces of human flesh littered the street after the attack, which also destroyed at least five nearby shops, witnesses said.

"It was a suicide attack which targeted Shiites but Sunni Muslims also fell victim since their mosque and some shops were also very close to the site," district police chief Mian Muhammad Saeed told AFP.

"We have found the head of the bomber, who came there on a motorbike," he said, putting the death toll at 24 with up to 55 others wounded.

Police said the bomb exploded as Shiites were leaving Friday prayers and Sunnis were going into their mosque for the main weekly sermon.

Hangu has long been a flashpoint for violence against minority Shiites, who make up an estimated 20 percent of Pakistan's population of 180 million.

The town is close to Pakistan's semi-autonomous tribal belt on the Afghan border where Taliban and Al-Qaeda-linked militants have carved out strongholds.

"The Shiite and Sunni mosques are very close to each other, and the explosion took place just as Shiites were coming out of the mosque and Sunnis were going into their mosque to say Friday prayers," said police official Imtiaz Shah.