Alexander Ponomarenko, the former owner of the Black Sea port of Novorossiisk, bought the complex for a sum close to $350 million (250 million euros) through a Cyprus based company that he controls, he told Kommersant business daily.

Whistleblower businessman Sergei Kolesnikov wrote an open letter to President Dmitry Medvedev in December alleging that the Italianate villa was being built for Putin's "private use."

An investigation by the liberal Novaya Gazeta found documents that linked the building in the Krasnodar region to the Russian government, although officials have denied this.

Earlier this month, environmental activists were briefly detained at the complex and posted a video on the Internet showing that police and federal protection service officers were guarding the construction site. The buyer of the complex, Ponomarenko, dismissed links to Putin as "rumours and journalists' fantasies" to Kommersant. He said he bought the complex from three owners after they asked him to invest because they had run out of money.

Ponomarenko said that he bought the complex, which he described as a "holiday centre", from Nikolai Shamalov, a friend of Putin, and two of his partners. Kolesnikov told the newspaper he believed the sale of the complex, which is still being constructed, was a reaction to his open letter.

He conceded that Ponomarenko bought it from the formal owners, but questioned where the money had come from to build the complex and extend infrastructure including roads.

"The main question remains: where did the money come from for construction. Secondly, the purchase does not change the situation around infrastructure, which the state built at its own expense," he told Kommersant.