A shell exploded in the barrel of a mortar during training maneuvers in central Russia on Friday, killing three Russian soldiers and injuring eight others, news reports said. Also Friday, an Mi-24 army helicopter crashed into a fuel truck in Siberia's Kemorovo region, severely injuring the aircraft's three crew members who were rushed to a hospital in critical condition, the ITAR-TASS agency quoted the Defense Ministry in Moscow as saying.