Two men, including one Australian, have been killed after an explosion on Thursday afternoon in the Cambodian province of Kampong Speu.

Three other men have been injured, including another Australian, though the injuries to the Australian man are said to not be serious. He has been treated at a hospital in Phnom Penh and he is able to walk.

There are conflicting reports about the cause of death of the two men. A Fairfax Media source on the ground said they died after a grenade exploded in what was described as tragic accident.

That same source said the two Australian men were military trainers, which the ABC has also reported.

A Reuters report suggested the pair may have been killed by a landmine during a joint training exercise on a Cambodian military base, while the Phnom Penh Post reported the tragedy occurred at a shooting range after the two dead men had attempted to pick up a Russian-made bomb.