PESHAWAR (AFP) - At least 13 people were killed when a gas cylinder exploded at a religious gathering in Pakistan's northwestern Swat valley on Thursday, officials said.

Another 67 people were wounded in the explosion which took place at a weekly meeting of the local Tableeghi Jamaat (preachers' party) at its primary centre in the outskirts of Mingora, the main town in the district, regional police chief Akhtar Hayat said.

"According to initial reports it was a gas cylinder blast," another senior police officer Gul Afzal Afridi told AFP.

There were around 1,500 people listening to the speech of a Muslim cleric at the centre when the cylinder exploded, he said.

A bomb disposal unit has been summoned to investigate though there was no sign of any explosives at the blast site, he added.

Internationally renowned Pakistani school girl campaigner Malala Yousafzai was shot in the head in Mingora last October in an attack claimed by the Pakistani Taliban.

She is now recovering and undergoing further treatment in Britain.

The Pakistani Taliban seized much of Swat during a 2007-2009 insurgency but the army declared the region back under control after an offensive in July 2009.