Edward Snowden's decision to release top secret documents from the National Security Agency (NSA) has drawn praise from Daniel Ellsberg, the former military analyst responsible for leaking the Pentagon Papers more than four decades ago. In a piece published Monday in the Guardian, Ellsberg hailed Snowden's leak as the most important in US history, arguing that it has exposed an "executive coup" against the US constitution.

Snowden, a 29-year-old former technical assistant at the CIA, claimed responsibility for the leak on Sunday, telling the Guardian that his decision was motivated by a sense of civic duty and a desire to safeguard constitutionally guaranteed rights to privacy. The documents, released last week, detail the widespread surveillance tactics deployed by the FBI and NSA, including a long-running government program called PRISM that allows the government to access user data on Google, Facebook, Apple, and a wide range of company servers.

"The United Stasi of America."

Ellsberg, 82, says the information revealed in Snowden's leak only underscores the government's ongoing effort to circumvent the US Constitution following the terrorist attacks of September 11th, 2001. Advances in technology and data sharing have only accelerated this erosion, Ellsberg notes, though he says Snowden's leak may finally encourage lawmakers to exercise more oversight and restraint when it comes to intelligence-gathering agencies.

"The NSA, FBI, and CIA have, with the new digital technology, surveillance powers over our own citizens that the Stasi – the secret police in the former 'democratic republic' of East Germany – could scarcely have dreamed of," Ellsberg writes. "Snowden reveals that the so-called intelligence community has become the United Stasi of America."

Ellsberg is arguably the most famous whistleblower in US history. In 1971, he gave confidential documents on the Vietnam War to the New York Times and the Washington Post, becoming the first person to be prosecuted under the Espionage Act. The so-called Pentagon Papers revealed that the US government had been drastically expanding military operations in Vietnam and Southeast Asia, and that four successive administrations had openly lied to the public about their true intentions.

The case against Ellsberg was ultimately thrown out after it was revealed that the government had illegally wiretapped his phone. The former analyst has since become an outspoken supporter of fellow whistleblowers including Bradley Manning, the army private and former intelligence analyst accused of leaking top-secret military documents to WikiLeaks.

"A lot of people will surely call him a traitor, but they’re mistaken."

In a separate piece for the Daily Beast, Ellsberg acknowledged that Snowden will likely face prosecution and criticism for his actions, though he says the leaker should be seen as a hero rather than a traitor.

"He could be kidnapped, he could be sent to Guantánamo, he could be executed," Ellsberg writes. "A lot of people will surely call him a traitor, but they’re mistaken. That’s an extremely unpleasant experience for someone who knows he’s a patriot, who’s certainly a patriot from what I know so far. Someone willing to sacrifice and die for his country."