The U.S. ranked 49th this year out of 180 countries included in the organization's World Press Freedom Index, joining the ranks of countries like Niger, Malta and Romania.

The decline from its position at No. 20 in 2009 has been spurred by the Obama administration's aggressive prosecution of whistleblowers, said Delphine Halgand, the organization's U.S. director.

"We consider that the Obama administration has launched a war against whistleblowers," Halgand said. "This year is a continuation of the concern we already expressed that national security protection has been more and more threatening freedom of information in the U.S."

The U.S. has prosecuted eight alleged whistleblowers under the Espionage Act, more than all previous presidential administrations combined, Halgand said.

Despite Obama's campaign pledge to make his administration one of the most transparent in history, reporters and press freedom watchdogs have continually slammed the administration as one of the least transparent and criticized its dogged efforts to plug leaks.

Reporters without Borders, an organization that works to protect journalists around the world, tied the U.S.'s drop in this year's rankings to the "judicial harassment" of James Risen, a New York Times reporter who last year stared down federal prosecutors pushing him to reveal the identity of an anonymous source.