At least 40 people have been killed and dozens more wounded after a blast ripped through a mosque in the Ghundai area of Khyber Agency, northwestern Pakistan.

The blast took place as people were leaving the mosque in Jamrud, Khyber's main town, after Friday prayers, with reports indicating that it was caused by a lone suicide bomber.

Local administration officials indicated that many of the wounded were in critical condition and that the death toll could rise.

Iqbal Khan, a local administrator, initially told the AP news agency that the number of wounded was 25, but local officials told Al Jazeera that it was closer to 80.

The AP reported that about 300 people had been attending the prayers.

"It was a suicide attack. The bomber was wearing about 8-10kg of explosives and was on foot. He detonated in the main prayer hall," said Khalid Mumtaz Kundi, the deputy chief of the district administration. He said that ball bearings had been found at the site of the blast.