Graham Stack in Kyiv -

Switzerland's state prosecutor is investigating Mykola Martynenko, an ally of Ukrainian Prime Minister Arseny Yatsenyuk, on suspicion of accepting CHF30mn in bribes, according to the Sonntagszeitung weekly. Swiss prosecutors confirmed that there was such an investigation in progress, without naming the suspect.

The reported move marks the first major corruption scandal to hit the new pro-EU government since it took office on an anti-corruption platform. The allegations regarding Martynenko are a blow to Yatsenyuk and his People's Front party, in which Martynenko is deputy head of the parliamentary group. People's Front nominated Martynenko to head the influential parliamentary fuel and energy committee, which has oversight of the nuclear industry.

Yatsenyuk's party refuted the allegations, calling them a "Russian conspiracy" and blaming it on Serhiy Leschenko, an MP in the eponymous party of Ukrainian President Petro Poroshenko. Leschenko is a respected former investigative journalist, who is believed to have alerted Swiss media to the allegations surrounding Martynenko.

People's Front accused Sonntagseitung of pro-Russian sympathies and said the aim of Leschenko's campaign was to "reintroduce Russian control over Ukraine's energy sector, which the Yatsenyuk government is trying to free from total dependence on the aggressor country". 

Martynenko is closely associated with Ukraine's nuclear power sector - the world's seventh largest, which produces 50% of the country's power - and he is regarded as the main political backer of the current head of Ukraine's nuclear power operator, Yury Nedashovsky. He has headed the parliamentary comittee on fuel and energy since 2006.

Ukraine's nuclear power sector is caught in a tug-of-war between Russia and the West, with Martynenko seen as a pro-Western influence in the sector, backing diversification of fuel and equipment supplies away from Russia. 

Martynenko is under investigation for allegedly accepting a bribe of CHF30mn in 2013 from Czech company Škoda JS, to supply equipment to Ukraine's nuclear power stations, according to the Swiss paper. 

In 2013, Martynenko said that purchasing the equipment from the Czechs would lessen Ukraine's dependency on Russia in the nuclear power sector. Later it transpired that the Škoda JS is owned by Russian engineering plant OMZ, a subsidiary of Russia's state nuclear power corporation Rosatom.

Škoda JS has denied any wrongdoing and has said it is not being investigated by either Czech or Swiss police, its management told the Czech News Agency.

Swiss prosecutors started their investigation when Swiss bank Hottinger reported suspicious large payments to Martynenko's account, according to Sonntagzeitung. A raid on Škoda JS by Czech police in December 2014 found documents substantiating the allegations, according to the paper. Swiss prosecutors have already questioned Martynenko over the alleged payments.