MOSCOW, June 25 (RIA Novosti) - A grenade blast killed one contract soldier and wounded another five during a tactical exercise in Russia's Far Eastern military district, a Defense Ministry's spokesman said on Wednesday.

"The explosion occurred during a regiment-level tactical exercise with live firing at the Zavitinsky training center in the Far Eastern military district," the source said.

A preliminary report indicates that a crew of a BMP-1 infantry fighting vehicle inadvertently fired a grenade at an observation post.

Russian Defense Minister Anatoly Serdyukov ordered an immediate investigation into the incident.

"[Defense Minister] Serdyukov ordered a special Defense Ministry commission to thoroughly investigate the incident and take immediate measures to provide the necessary medical assistance to the wounded soldiers," the spokesman said.

The wounded are being treated at a regional military hospital.

A total of 442 servicemen died in accidents and other non-combat incidents in the Russian Armed Forces in 2007. Twenty-three soldiers died due to negligence.

No statistics on the number of non-combat fatalities since the beginning of 2008 have been provided by the Defense Ministry yet.