"The exact number of enemy casualties is unknown but pilots flying overhead estimated that approximately 40 to 50 insurgents were killed," the statement said.
One Afghan soldier was killed and three were wounded, it added.
Clashes erupted before dawn Monday at a border post between Khost province and Pakistan's rugged western tribal region, where al Qaeda fighters have taken sanctuary and run militant training camps following the defeat of their Taleban hosts.
About 50 suspected Taleban insurgents attacked the post at 2:00 am Monday (2130 GMT Sunday) with rocket-propelled grenades, machineguns and mortars.