The father of former US spy agency contractor Edward Snowden says he will not fly to Russia to serve as an "emotional tool" in the United States' efforts to persuade his son to surrender.

Lonnie Snowden told the Washington Post that FBI officials had not been able to guarantee if he would be allowed to see his son, who faces espionage charges in the US for exposing secret surveillance programs.

"I said, 'I want to be able to speak with my son. ... Can you set up communications?' And it was, 'Well, we're not sure,'" Lonnie Snowden told the Post. "I said, 'Wait a minute, folks, I'm not going to sit on the tarmac to be an emotional tool for you.'"

The elder Snowden earlier told state-owned Russian 24 television the FBI had suggested a "few weeks ago" that he should travel to Moscow to talk to his son.

Edward Snowden, whose exposure of the surveillance raised questions about intrusion into private lives, has been stuck in the transit zone of Moscow's Sheremetyevo airport since arriving from Hong Kong more than a month ago.

His father has had no direct contact with him. "I received this suggestion (from the FBI to travel to Moscow) a few weeks ago, and I have yet to decline it," Lonnie Snowden said.

He said he believed his 30-year-old son, who has applied for temporary asylum in Russia after the cancellation of travel documents meant he was unable to travel to Latin America, was better off in Moscow.

"If he wants to spend the rest of his life in Russia, I would agree. I am not against it," he said. "If I were in his place, I would stay in Russia, and I hope that Russia will accept him."

Lonnie Snowden again said he did not think his son would get a fair trial in the United States because of "what happened in the last 5-6 weeks."

He thanked President Vladimir Putin and his government for the "courage" they have shown in keeping his son safe.

Addressing his son, he said: "Your family is well and we love you."

He added that "I hope to see you soon, but most of all I want you to be safe."

The Russian lawyer helping Edward Snowden, Anatoly Kucherena, told the program he thought his asylum request would be granted "in the coming days" and that the US had failed to send an official extradition request.

"If you want (to have Snowden handed over), you should adhere to the law, so send, according to existing rules of cooperation between states, a corresponding legal document, correctly filled out. But there is no such thing," said Kucherena, a lawyer who is close to the Kremlin. "Just saying 'hand him over' is absolutely dishonorable and incorrect."

The lawyer said he and Snowden agreed over the telephone that "I will put together an invitation for his father to come to Russia."

Yesterday, Britain's Guardian newspaper published further details of documents handed over by Snowden on secret monitoring of e-mails by the NSA.

Kucherena said Snowden handed the documents over before he arrived in Moscow.