The 82-year-old father of former Russian oil tycoon Mikhail Khodorkovsky has been questioned by investigators about the 1998 killing of a Siberian mayor.

Russian investigators announced in June that they were reopening the investigation of the murder of Nefteyugansk Mayor Vladimir Petukhov and considered Mikhail Khodorkovsky a prime suspect. Khodorkovsky and his associates have denied involvement in the killing.

Khodorkovsky spent 10 years in prison on charges of tax evasion and embezzlement seen as punishment for challenging President Vladimir Putin's power. Since his 2013 release, he has continued to oppose Putin from exile in Switzerland.

His father's lawyer, Sergei Badamshin, described Thursday's questioning as "shameless pressure" on Mikhail Khodorkovsky.