Two rights groups launched a stinging critique Wednesday on Russia's freedom of expression record, citing a heavy clampdown on critics and activists since Vladimir Putin returned to the presidency.

The reports by Amnesty International and Human Rights Watch highlight changes to the law that they say have helped authorities stifle dissent.

"In the year since Vladimir Putin's return to the presidency in May 2012, the Russian government has unleashed a crackdown on civil society unprecedented in the country's post-Soviet history," Human Rights Watch said in its report.