Russia's main domestic security agency has searched the offices of a company controlled by the billionaire owner of U.S. basketball team Brooklyn Nets, Mikhail Prokhorov.

The Federal Security Service, the main KGB successor agency, said Friday the searches were part of a probe into alleged tax evasion. It added that the investigation is continuing.

Some Russian media have speculated that the searches could have been aimed at pressuring Prokhorov into surrendering control over his media assets. They include RBC, an online newspaper that has published reports of the Kremlin, including a detailed account of the so-called Panama Papers.

The searches on Thursday went on just as President Vladimir Putin held his annual call-in TV show. Putin's spokesman Dmitry Peskov strongly denied any link between the searches and Prokhorov's media assets.