Four security personnel were killed and five others injured when heavily armed militants attacked military personnel in the tribal region of South Waziristan, military spokesman said on Saturday.

The Inter-Services Public Relations stated that nine militants were also killed during a search operation carried out in the town located on the border of restive South and North Waziristan region, DawnNews reported.

It informed that four security personnel were killed in the exchange of fire with militants. Military sources said the incident took place in the Pre Ghar area on the border between North and South Waziristan tribal regions.

Security forces are advancing in far-flung areas of South Waziristan. They have taken control of most of the strongholds of Taliban in the areas.

The conflict zone is remote and off-limits to journalists making it difficult to verify the army's claims, including the number and identity of those killed.

The sources said security personnel were facing resistance in some areas and sporadic incidents of attacks and exchange of fire were taking place.

The semi-autonomous tribal areas on the Afghan border have for years been a hideout for militants of all stripes, including Al Qaeda and the Pakistani Taliban as well as foreign fighters such as Uzbeks and Uighurs.

Pakistan began a long-awaited push to clear insurgent bases from North Waziristan last June after a bloody Taliban attack on Karachi airport finally sank faltering peace talks.