Russia on Tuesday added jailed Kremlin critic Alexei Navalny to a list of "terrorists and extremists", as authorities continue a clampdown on the opposition.

Navalny and several of his allies, including key aide Lyubov Sobol, appeared Tuesday on a database of banned individuals compiled by the Federal Service for Financial Monitoring (Rosfinmonitoring).

According to Navalny's Anti-Corruption Foundation -- which was declared extremist and shut down last year -- nine other Navalny allies were added to the list on Tuesday.

The decision puts them on a par with right-wing nationalist groups and foreign terrorist organisations, including the Taliban and the so-called Islamic State group.