Russia is observing a national day of mourning for the more than 125 people believed killed when a tourist boat sank on the Volga River Sunday.

Rescuers have recovered 64 bodies so far and say there is no hope of finding anyone else alive. Many of the victims were children who were in a playroom on the aging cruise ship, the Bulgaria, when it sank.

President Dimitry Medvedev on Monday demanded an investigation into the sinking. He called the vessel “decrepit” — one of a “number of old rust tubs we have sailing.”

U.S. President Barack Obama expressed his condolences on the accident in a telephone conversation with Mr. Medvedev Monday.

The Bulgaria was built in Czechoslovakia in 1955. It was meant to carry 120 people, but 208 were on board when it sank during a storm near Kazan, in the republic of Tatarstan.

Survivors say the overloaded boat started listing to one side within moments of setting sail. Survivors were quoted as saying the ship sank within three minutes, giving the crew little time to take action.