Six Russian soldiers were killed on Saturday when their armoured troop carrier overturned in Georgia's breakaway region Abkhazia, local news agencies said.
"Several possible reasons behind the accident are being pursued, among them a sudden mechanical fault and the appearance of an unexpected obstacle on the road," Colonel Igor Konashenkov told Interfax.
Abkhazia won effective independence from Georgia in a 1992-3 war. Russian peacekeepers have been monitoring the fragile peace since the end of military conflict.
Tbilisi says Russia armed the Abkhaz rebels and it has accused Moscow of meddling in the conflict ever since. Russia props up Abkhazia's devastated economy by paying pensions, handing out passports and allowing cross-border traffic.