A Swedish prosecutor has begun an investigation into share options given to Foreign Minister Carl Bildt, to see if they could be construed as a bribe.
Carl Bildt said the shares were a legitimate reward for his work
Mr Bildt received the options as part of his previous job, on the board of an energy firm linked to Russia's Gazprom.
Gazprom wants to build an underwater pipeline between Russia and Germany, passing close to Swedish territory.
Mr Bildt welcomed the inquiry and said the shares, which he sold for $690,000 (£355,000), were a legitimate reward.
He rejected suggestions it would undermine his ability to deal fairly with Russia.
Mr Bildt resigned from the board of oil investment company Vostok Nafta when he became foreign minister in October.
Prosecutor Christer van der Kwast said the share options could be considered a bribe if they were "an improper benefit... in connection with his new role as a minister", Swedish newspaper Svenska Dagbladet said.