Sayano-Shushenskaya (Russia), Aug 18 (RIA Novosti) The toll in an accident at Russia's largest hydropower plant has risen to 12, with 64 people still unaccounted for, the country's emergencies minister said Tuesday.

'The fate of 64 people is still unknown,' minister Sergei Shoigu told reporters at the south Siberian Sayano-Shushenskaya power station, where he is coordinating rescue and clean-up work. Some 1,200 rescuers are working at the scene.

Emergencies officials said 15 people were also injured early Monday when two water ducts collapsed at the plant, flooding a turbine hall.

Earlier reports said the disaster could have been triggered by the explosion of an oil transformer while workers were carrying out repairs.

Russian prosecutors said Tuesday the accident was not a result of a terrorist act. 'Experts have not found any traces of explosives at the scene,' the investigation committee said in a statement.

The flooding has now been stopped, Shoigu said.

He said divers were searching for bodies, and robots and other equipment would be used to monitor the river surface and check the damaged facilities.

Emergency workers are also trying to deal with an oil slick that took place at the Yenisei river after the accident.

Four people earlier reported missing were found late Monday. One was discovered in a state of shock in the station's underground facility, one was retrieved from the water, and two others were found at their homes.