The federal Investigative Committee said law enforcement officers searched the office of Kirov region governor Nikita Belykh as part of a criminal investigation into the alleged theft of 90 million roubles ($3 million).

Belykh denied any wrongdoing and said he was cooperating with the investigation.

A former moderate opposition party leader, Belykh was appointed in 2009 by then-President Dmitry Medvedev in what was seen as an effort to appease liberals pushed to the margins during Putin's 2000-8 presidency and ally them with the Kremlin.

"The searches in Nikita's office are a clear sign of the end of the 'Medvedev thaw'," Maria Gaidar, a critic of Putin and a former deputy to Belykh, said on Twitter. Putin returned to the presidency in May after four years as prime minister.

Opposition leaders accuse the Kremlin of using the court cases and criminal investigations to put pressure on Putin's critics during his new six-year term, but the president's spokesman has denied this.

Boris Nemtsov, an opposition leader who preceded Belykh as head of a liberal pro-business party in the mid-2000s, said the search was aimed not at Belykh directly but at Alexei Navalny, who has helped organise protests against Putin and has been charged in a separate case of theft in the Kirov region.

The Investigative Committee said police, FSB security forces and federal investigators were searching for documents related to the sale of a 25.5 percent state share in a distillery for some 90 million roubles less than its market value, which the committee said was about twice that figure.