The explosion occurred while military personnel were transporting munitions at a base, said Guard spokesman Gen. Ramazan Sharif. The site is located outside Bidganeh village, 25 miles (40 kilometers) southwest of the capital.
The Guard is Iran's most powerful military force.
"My colleagues at the Guard were transporting ammunition at one of the depots at the site when an explosion occurred as a result of an accident," Sharif said.
At least 27 Guard members were killed, state TV reported. The broadcast said 16 other soldiers were injured and hospitalized. Sharif said some of them were in critical condition.
Lawmaker Parviz Soroori ruled out sabotage.
"No sabotage was involved in this incident. It has nothing to do with politics," Soroori was quoted as saying by the parliament's website, icana.ir.