ALMATY (Reuters) - Security forces blocked several downtown streets and cordoned off one of the squares in Kazakhstan's biggest city Almaty on Wednesday as an opposition group planned to stage protests, a Reuters correspondent reported from the scene.

       The oil-rich Central Asian nation was shaken this month by the worst bout of violence in its post-Soviet history during which at least 225 people were killed, most of them in Almaty.

       On Wednesday, a group led by Mukhtar Ablyazov, a former Kazakh banker turned government critic in exile, said it would hold protests outside local government buildings in major cities throughout the country of 19 million.

       A Kazakh court has ruled Ablyazov's political movement, Democratic Choice of Kazakhstan, was extremist.

       Police in Almaty said they were carrying out an "anti-terrorist operation".

       (Reporting by Pavel Mikheyev and Mariya Gordeyeva; Writing by Olzhas Auyezov; Editing by Michael Perry)