When members of Europe's leading human rights forum voted this month to create a "platform for dialogue" with exiled opponents of Russian President Vladimir Putin, the move went largely unreported by the world's media.

But Russia's FSB security service was paying close attention to the resolution by the Parliamentary Assembly of the Council of Europe (PACE). On Tuesday, without waiting for PACE to select and name its Russian partners, the FSB cited the initiative as part of its justification for opening a new criminal investigation into 23 dissidents based outside the country, whom it accused of forming a "terrorist organization" and plotting to seize power.

Former oil tycoon Mikhail Khodorkovsky was named as the ringleader of the alleged plot. He had said he would like to participate in the PACE forum.