Russian conscripts often complain of bullying during training

A defence spokesman said the men - from a helicopter training unit - had been summoned to a local prosecutor's office on suspicion of theft on Tuesday.

He said the four had almost completed their two-year military service. A commission from Moscow is flying to Saratov to investigate the deaths.

A human rights group suggested the four may have been murdered.

Valentina Melnikova, the executive secretary of the campaigning Committee of Soldiers' Mothers in Russia, said she was certain of it.

"I'm 100% sure it was murder, and most probably murder linked to some money or other: either debts or complaints from some officers or civilians," she said.