MOSCOW - The confirmed death toll in a Russian riverboat accident reached 100 on Wednesday after divers recovered more bodies from the sunken vessel, an Emergency Situations Ministry official said.

Twenty-nine of the 208 people who were aboard the ageing, overcrowded boat when it sank in the Volga River on Sunday were still unaccounted for and feared dead. Officials say 79 people survived Russia's worst river accident since 1983.

The Bulgaria, a 79-metre river cruiser built in 1955, listed onto its right side during a thunderstorm and sank in minutes in a broad stretch of the Volga in the Tatarstan region, trapping many passengers inside, survivors said.

The precise cause of the disaster was not clear, but prosecutors said the boat, which they said lacked a license to carry passengers, was already listing to the right when it left port on Sunday and had engine trouble.

Emergency officials said the boat was meant for up to 140 people but was carrying 208, including 25 unregistered passengers.

The confirmed dead included 17 children, but emergency officials said on Tuesday that divers had seen about 50 bodies, most of them children, in a recreation room on the sunken boat.