The militants launched their attack overnight on Talab check post in mountainous Sararogha district of South Waziristan region, they said.
"Five soldiers were killed and one is missing," a security official said, requesting anonymity.
Another security official confirmed the the attack, saying information came late as the check post is in a remote mountainous area some 50 kilometres (30 miles) northeast of the region's capital, Wana.
Pakistan last year sent 30,000 troops into South Waziristan to destroy Taliban strongholds in the the lawless region.
Sararogha was a stronghold of Baitullah Mehsud, the founder of Tehreek-e-Taliban Pakistan (TTP), who was killed in a US drone strike in August last year. The group is now led by Hakeemullah Mehsud.
The TTP, which operates out of Pakistan's semi-autonomous districts, is blamed for the deaths of thousands of people in attacks across Pakistan in recent years.
Washington says Pakistan's tribal belt, which lies outside direct government control, is an Al-Qaeda headquarters and a stronghold for militants plotting attacks on US-led troops fighting against the Taliban in Afghanistan.
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