MOSCOW, August 25 (RIA Novosti) - Russia's industrial safety watchdog Rostekhnadzor will prepare a report by the end of September on the cause of an accident at Russia's largest power station last week, the head of the watchdog said on Tuesday.

Seventy-one people were killed and four people are still missing following the accident at the Sayano-Shushenskaya plant on the Yenisei River in south Siberia, which occurred on August 17 during repair work. A surge of water burst into the turbine hall, completely destroying three turbines and flooding several lower stories of the plant.

"I am sure that we will have reached a conclusion on the cause of the accident by the end of September," Nikolai Kutin told a RIA Novosti news conference.

The official added that that an inspection of the plant conducted by Rostekhnadzor last year did not reveal any technical failures or breaches at the station.

Kutin praised emergencies ministry workers, involved in the rescue operation, but criticized plant management. "In the first 24 hours, the station's personnel and leadership were disorganized and not up to the job," he said.

Dam owner RusHydro has said repairing the damage could take up to two years to carry out, and Energy Minister Sergei Shmatko estimated the cost could run to at least 40 billion rubles ($1.2 billion).

The Russian government has pledged compensation of 1 million rubles ($31,500) to the victims' family, and 100,000 rubles to each survivor. RusHydro is also due to pay a further 1 million rubles in compensation, although relatives are demanding 5 million rubles in damages.