Pakistan's DawnNews quoted local administrator Fazal Khan as saying there was some evidence the bombing of the Jamrud mosque in Ghundi village was a suicide attack.
No group immediately claimed responsibility for the bombing, but Pakistan's tribal belt is a hotbed of militant activity, as well as sectarian rivalry.
Hundreds of people were at the mosque for Friday prayers when the bomb exploded, according to media reports. Some reports said up to 500 people were inside the mosque at the time of the blast.
The entire mosque collapsed following the blast, according to the media reports and many people were said to have been buried under the debris of the collapsed mosque.
Pakistan’s tribal belt is a hotbed of militant activity, as well as sectarian rivalry.
Also on Friday, A suspected US drone strike in the South Waziristan tribal region killed at least two people, DawnNews reported. The region was largely under Pakistani Taliban control until the Pakistani army launched an operation there in October 2009.
The drone attacks, started by the CIA in 2004 to eliminate militants have been ramped up over the past three years, with a record 118 strikes last year and over 50 so far in 2011. More than 2,500 hundred people have been killed in suspected drone strikes, which are rarely confirmed or denied by the US.