A suicide bomber targeted a Shia Muslim mosque in northwest Pakistan yesterday, killing 21 people and wounding up to 50 as worshippers poured out of weekly prayers, officials said.

The bomber detonated explosives packed into a motorcycle in a narrow lane containing both the Shia 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 Shias 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.

Police said the bomb exploded as Shias 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 Shias, who make up an estimated 20 percent of Pakistan’s population of 180 million.

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