Transparency at Russia's state nuclear energy concern Rosatom has improved over the past year, but much remains to be done at the behemoth, Transparency International said on Friday.

"We have noted improvements... in comparison with 2010. (It) has also become more transparent from the point of view of information," Elena Panfilova, who head TI's Russia office, told a press conference.

But "there still remains a lot to be done, a lot to change," she said.

"A number of questions related to transparency and corruption factors have not been resolved," TI said in a report on Rosatom released at the press conference.

A year ago, TI said Rosatom was a "state within a state" that conducted rigged auctions and overpaid for contracts that could have been struck at a lower and more competitive price.

Rosatom succeeded the Soviet Union's Ministry of Nuclear Energy and Industry in 1992. It was transformed into a state corporation in 2004.

Rosatom also controls nuclear weapons companies and oversees the construction and running of Iran's first nuclear power plant.