A spokesperson for the U.S. State Department says Washington is "troubled" by Russia's banning of a pro-democracy charity fund founded by U.S. billionaire and philanthropist George Soros.

Spokesperson Mark Toner said the November 30 designation of the Open Society Foundations and the Open Society Institute Assistance Foundation as so-called "undesirable" organizations "will only further restrict the work of civil society in Russia for the benefit of the Russian people."

A spokesperson with Russia's Prosecutor-General's Office said the activities of the two branches of Soros's charity network represent a threat to both state security and the Russian constitution.

In a statement issued after the decision was announced, Toner said the move is yet another example of Russia’s "growing crackdown on independent voices and a deliberate step to further isolate the Russian people from the world."

The Open Society Foundations said in a statement posted on their website that they were "dismayed" by Russia's decision.

"Contrary to the Russian prosecutor's allegations, the Open Society Foundations have, for more than a quarter-century, helped to strengthen the rule of law in Russia and protect the rights of all," the November 30 statement said.

“We are confident that this move is a temporary aberration; the aspirations of the Russian people for a better future cannot be suppressed and will ultimately succeed,” the statement quoted Soros who chairs the Open Society Foundations as saying.

Based on reporting by Reuters and Interfax