The move was revenge by the authorities for an article in which the activist, Larisa Arap, 48, criticised practices in children's mental health wards, Mr Kasparov said.
Ms Arap, a member of Mr Kasparov's United Civil Front, is being medicated against her will, he claimed.
Activists say this is not the first case of politically motivated, enforced admission to hospital in President Vladimir Putin's Russia, and have condemned the move as redolent of the Soviet era. Mr Kasparov said: "It could happen if you attack the interests of the local Gazprom, the local military base, the local medical mafia. Attacking the interests of local bureaucrats is a terrible risk, because they don't stop at anything to get their own back." London Independent