Former US defense contractor Edward Snowden is seen during an interview with "NBC Nightly News" anchor and managing editor Brian Williams in Moscow in this undated handout photo released May 28, 2014. [Photo/Agencies]

WASHINGTON - Former US spy agency contractor Edward Snowden told a US television interviewer he would like to go home from asylum in Moscow, but that if necessary he would seek to extend his stay in Russia.

Edward Snowden says he was trained 'as a spy'

US officials said he was welcome to return to the United States if he wanted to face justice for leaking details of massive US intelligence-gathering programs.

"If I could go anywhere in the world, that place would be home," Snowden told NBC Nightly News anchor Brian Williams in an excerpt from the interview that aired on Wednesday.

Asked how anxious he was to make a deal to return to the United States, Snowden replied: "My priority is not about myself. It's about making sure that these programs are reformed - and that the family that I left behind, the country that I left behind - can be helped by my actions."

He added that if his one-year asylum in Russia, which expires on Aug. 1, "looks like it's going to run out, then of course I would apply for an extension."

Snowden, who fled to Hong Kong and then Moscow last year, is believed to have taken 1.7 million computerized documents. The leaked documents revealed massive programs run by the NSA that gathered information on emails, phone calls and Internet use by hundreds of millions of Americans.

He was charged last year in the United States with theft of government property, unauthorized communication of national defense information and willful communication of classified intelligence to an unauthorized person.

Secretary of State John Kerry invited Snowden to "man up and come back to the United States."

"The bottom line is this is a man who has betrayed his country, who is sitting in Russia, an authoritarian country where he has taken refuge," Kerry told the CBS "This Morning" program on Wednesday.

"If he has a complaint about what's the matter with American surveillance, come back here and stand in our system of justice and make his case," Kerry said.

Saying he saw himself as a patriot, Snowden said: "The reality is the situation determined that this needed to be told to the public. The Constitution of the United States had been violated on a massive scale.

US officials also fired back at Snowden's comments in an excerpt from the NBC interview that aired on Tuesday in which he said he was trained as a spy and had worked undercover overseas for the US government.

Asked by CNN if that were true, White House national security adviser Susan Rice replied: "No."