Russia's financial watchdog added chess grandmaster and political activist Garry Kasparov to its list of "terrorists and extremists" on Wednesday.

The 60-year-old former world chess champion has been a longtime opponent of President Vladimir Putin and has repeatedly spoken out against Russia's military offensive in Ukraine.

The Rosfinmonitoring watchdog is responsible for combatting money laundering and terror financing, and those listed can have their bank accounts seized.

Rosfinmonitoring added Soviet-born Kasparov to its database of "terrorists and extremists" without giving a reason.

Rights groups say the label is another tool the Kremlin uses to silence its critics, along with the "foreign agent" term it applies to people it sees as enemies of the state.

Kasparov is widely regarded as one of the world's greatest chess players and has lived in the United States for over a decade, where he has focused on political activism.

In February last year he urged the West to keep up its support for Kyiv and said Ukraine had to defeat Moscow as a "pre-condition" for a democratic transition in Russia.