MOSCOW, April 6 - The operator company's indecision and slowness – not an earthquake or a tsunami - caused the disaster at the Fukushima nuclear power plant to become a catastrophe, Oleksandr Kovalenko, ex-deputy head of the Chernobyl nuclear power plant, told Interfax.

"In my opinion, the operator company's confusion and lack of action caused a nuclear accident of medium severity to deteriorate into a real catastrophe," said Kovalenko, who was in charge of the information and international relations department of the government commission for dealing with the aftermath of the Chernobyl nuclear disaster.