Shahidullah Shahid said the troopers died when their convoy was hit by a roadside bomb in the Jalrez district, about 40 km west of Kabul.
At least one vehicle was destroyed in the blast, Shahid said.
A Taliban spokesman, Zabihullah Mujahid, claimed a higher death toll, saying five US soldiers were killed in the attack.
NATO and US forces could not be reached for comment on the incident in Maidan Wardak, which has been the scene of increasing Taliban attacks over the past two years.
Meanwhile, the NATO-led International Security Assistance Force (ISAF) said in a statement that one of its soldiers was killed in eastern Afghanistan in another roadside bombing.
The ISAF did not give details about the nationality of the soldier or a more exact location of the explosion.
