Edward Snowden speaks via video link from Russia during a news conference in New York City on Wednesday. (Brendan Mcdermid/Reuters)

Human rights activists have launched a campaign calling on President Obama to pardon Edward Snowden, a former National Security Agency contractor charged with espionage after he leaked documents revealing U.S. surveillance programs of breathtaking scope.

Snowden, who has been living in Moscow under a grant of political asylum since 2013, has been credited with sparking a global debate about the proper limits of government surveillance. He has also been accused of disclosing details of classified programs that have endangered national security in violation of the Espionage Act of 1917.

As a result of one document he revealed, the government was forced to acknowledge a program of bulk collection of all U.S. customers’ phone call data — times, dates and numbers dialed, but not content. That launched two years of debate that culminated in legislation outlawing such mass harvesting of phone records.

But other documents provided to reporters disclosed details that led, for instance, to the shuttering of what Director of National Intelligence James R. Clapper described as “the single most important source of force protection and warning for our people in Afghanistan.” It was an apparent allusion to an NSA program that recorded all cellphone calls in that country.

Snowden, speaking from Moscow by video link to a news conference in New York City, said that he would return to the United States if he felt he would receive a fair trial. But, he said, the Espionage Act does not permit a public interest or whistleblower defense.

“This World War I-era law does not distinguish between those who freely give information to journalists in the public interest or spies who sell it to a foreign power for their own [gain],” he said.

The activists at the news conference called on Obama to act before he leaves office in January. “Edward Snowden’s case presents one for President Obama to use the presidential power of pardon proudly and unequivocally in recognition of one of the most important acts of whistleblowing in modern history,” American Civil Liberties Union Executive Director Anthony Romero said at the news conference Wednesday.

The Obama administration has rebuffed efforts so far to win a pardon for Snowden, 33. Last year, Lisa Monaco, Obama’s advisor on homeland security and counterterrorism, said in response to a We the People petition on behalf of Snowden: “If he felt his actions were consistent with civil disobedience, then he should do what those who have taken issue with their own government do: Challenge it, speak out, engage in a constructive act of protest, and — importantly — accept the consequences of his actions.”

A Justice Department spokesman on Wednesday said the department’s position has not changed since charges were brought in June 2013. “Mr. Snowden should return to the United States and face the charges filed against him,” spokesman Marc Raimondi said. “It is important to remember Mr. Snowden is not a whistleblower. He is accused of leaking classified information, and there is no question his actions have inflicted serious harms on our national security.”

The campaign, launched Wednesday and called Stand up for Snowden, urged people to sign a petition on its Pardonsnowden.org.