At least four people were killed and six others injured on Friday when a bomb blast rocked Pakistan 's northwestern tribal region of South Waziristan, local media reported.

According to the reports, the blast took place outside the office of a former militant commander Maulvi Abbas in the vegetable market of Wana district of South Waziristan, Pakistan's tribal region bordering Afghanistan.

The nature of the blast was not known yet. The blast also destroyed eight shops in the market. Shortly after the blast intensive firing was also heard near the spot.

Eyewitness told media that the bomb exploded with a big bang as it killed four people on the spot including the militant commander and his two companions while injuring six others.

Earlier reports said that three people were killed and 21 people injured in the blast in North Waziristan area but later security official told media that four people were killed and only six injured in South Waziristan.

No group or militant organization has claimed responsibility for the attack yet.