Russia has arrested Semyon Mogilevich, a suspected organised crime boss, for large-scale tax evasion, moving against a man wanted by the FBI for racketeering, money-laundering and wire fraud.

Mr Mogilevich, a 61-year-old Russian citizen, is also believed by Ukrainian politicians to play a significant role in the multi-billion-dollar gas trade between Moscow and Kiev.

About 50 armed commandos wearing masks detained Mr Mogilevich and Vladimir Nekrasov, the owner of Arbat Prestige, a leading Moscow cosmetics retailer, as they left a Moscow office building on Wednesday evening, Mr Mogilevich's lawyer, Alexander Pogon-chenkov, said on Friday. They are now in prison after a Moscow court on Thursday sanctioned their arrest, he said.

A spokeswoman for the interior ministry said Mr Nekrasov and Mr Mogilevich, who is currently going by the name of Sergei Schnaider and who has as many as seven different surnames, were detained as part of a criminal case into large-scale tax evasion. She declined to disclose the sum.

Mr Mogilevich has been living freely in Moscow despite being on the FBI's most wanted list since 2003. Robert Mueller, FBI chief, in a 2005 speech accused Mr Mogilevich of setting up a "powerful organised crime enterprise" that "engaged in drug and weapons trafficking, prostitution and money laundering, and organised stock fraud in the United States and Canada in which investors lost over $150m [€102m, £76m]".

Mr Mogilevich's lawyer in Israel, Zeev Gordon, said Mr Mogilevich denied any wrongdoing. Alexander Dobrovinsky, Mr Nekrasov's lawyer, said his client denied any wrongdoing and any business ties with Mr Mogilevich.

Oleksandr Turchinov, Ukraine's first deputy prime minister, led an investigation in 2005, when he headed the security services, into possible links between Mr Mogilevich and Rosukren-ergo, the Swiss-registered gas trader, which has a monopoly on gas supplies to Ukraine. The inquiry was not completed. Rosukren­ergo is jointly owned by the Russian state-run Gazprom and a Ukrainian businessman, Dmytro Firtash.

On Friday, a spokesman for Mr Firtash said he was on a business trip and unavailable for comment. He added that Group DF, Mr Firtash's holding company, had never had any interest in Arbat Prestige nor any links with Mr Nekrasov or Mr Mogilevich. Mr Gordon said Mr Mogilevich denied any ties with Rosukrenergo.

Mr Mogilevich's arrest this week sparked questions about a possible shake-up in the Russia-Ukraine gas trade. Russia's state-run television gave wide airing to his arrest.

Yulia Tymoshenko, who at the end of last year won back her position as Ukraine's prime minister, has long fought to remove Rosukrenergo from the gas business, calling it a "criminal canker" on the side of the Ukrainian-Russian gas trade.

Dmitry Medvedev, Vlad­imir Putin's preferred successor as Russian president and chairman of Gazprom, called last year for Ros­ukrenergo to be eliminated.

Stanislav Belkovsky, a political adviser who worked as an aide to Ms Tymo-shenko in 2005, said Mr Mogilevich's arrest over the tax evasion allegations was "just an excuse".

"The real reason is gas," he said, adding that Ms Tymo­shenko had been lobbying Kremlin factions jealous of Rosukrenergo's status.

Mr Pogonchenkov said he could not rule out the possibility that the arrest of his client was connected with Ms Tymoshenko's appointment. "I can't exclude this," he said. "This is an advantageous step for Tymoshenko."

But he could not confirm any details of Mr Mogilevich's interests in the gas business, saying only that he was a criminal lawyer and did not delve into Mr Mogilevich's corporate business. Mr Gordon ruled out any link. "I don't believe it's connected to gas. If it's about gas, why arrest Nekrasov?" he said.

Mr Nekrasov was arrested on suspicion of orchestrating a tax evasion scheme by three suppliers to Arbat Prestige, while Mr Mogilevich was arrested on suspicion of helping mastermind the scheme, Mr Pogon-chenko said.

Mr Pogonchenkov said his client had maintained a close friendship with Mr Nekrasov over the past three years, but otherwise had nothing to do with Arbat Prestige.

"My client is not a shareholder or an employee of Arbat Prestige. His only contact with Arbat Prestige is when he goes there to shop and when he sometimes sees Nekrasov," he said. "They have not produced one bit of evidence."

Russian prosecutors must file charges within 10 days of the pair's arrest