Russia's transportation watchdog has attributed the July 10 cruise ship accident accident on the Volga River to safety violations and a poorly trained crew.

The Bulgaria double-decked riverboat, with more than 200 passengers on board, sank during a storm in a stretch of the river in the Russian Republic of Tatarstan, leaving 120 people dead, according to reports of RIA Novosti.

"The ship sank because it lost balance in the storm after water flowed into open portholes," the transport watchdog said in its investigative report, adding that this had made the ship lean to the right and eventually sink.

Safety regulations require that all portholes, including the ones in passenger rooms, be closed before a vessel starts moving.

"During the inspection of the sunken ship, divers discovered that 27 portholes were opened on the left side of the vessel and 11 on the right side," the Federal Service for the Oversight of Transportation said.

Shortly after the tragedy, media reports showed that the riverboat, built in 1955, had last undergone an overhaul 30 years ago and had no license to carry passengers.

It was also revealed to have been seriously overloaded when it left port on its fateful voyage with only one of its two engines operable.

The transport watchdog further said that the captain had failed to inform navigation traffic controllers of the cruise, despite a storm warning.

Two people have already been charged over the sinking of the ship.

Svetlana Inyakina, the general director of the company that rented the cruise boat, and river fleet inspector Yakov Ivashov, who certified that the vessel was fit to sail, may face prison sentences if found guilty.