The United States has told Russia it will not seek the death penalty nor torture fugitive intelligence leaker Edward Snowden, in an attempt to convince Moscow to turn him over.

The assurances came in a letter obtained by AFP Friday that Attorney General Eric Holder sent to Russian Justice Minister Alexander Konovalov.

"We understand from press reports that Mr. Snowden has filed papers seeking temporary asylum in Russia on the grounds that if he were returned to the United States, he would be tortured and would face the death penalty," Holder wrote.

"These claims are entirely without merit."

Snowden, whom Washington wants to put on trial for disclosing details of massive US surveillance, has been marooned at Moscow's Sheremetyevo airport for more than a month amid uncertainty about his future.

The case has further strained relations between Washington and Moscow, although a Kremlin spokesman indicated Friday that Snowden's fate is not on President Vladimir Putin's immediate agenda.

The White House has voiced strong opposition to Snowden's request for safe haven in Russia and has criticized Moscow for providing him with a "propaganda platform."

In the letter dated Tuesday, Holder said the charges against the 30-year-old do not carry the possibility of the death penalty and that "the United States would not seek the death penalty even if Mr. Snowden were charged with additional, death penalty-eligible crimes."

Holder also stressed to Konovalov that the former National Security Agency contractor would not be tortured and would receive a fair trial back home.

"Torture is unlawful in the United States," he wrote.

"If he returns to the United States, Mr. Snowden would promptly be brought before a civilian court convened under Article III of the United States Constitution and supervised by a United States District Judge."

Snowden would be appointed or could retain counsel, and any questioning would be conducted only with his consent, he added.

"Mr. Snowden would have the right to a public jury trial; he would have the right to testify if he wished to do so; and the United States would have to prove his guilt beyond a reasonable doubt to a unanimous jury," Holder wrote.

"If convicted, Mr. Snowden would have the right to appeal to the United States Court of Appeals."

Holder said Washington believes "these assurances eliminate these asserted grounds for Mr. Snowden's claim that he should be treated as a refugee or granted asylum, temporary or otherwise."

Holder also said that, despite news reports and Snowden's belief to the contrary, he is able to travel and is eligible for a "limited validity passport."

"Despite the revocation of his passport on June 22, 2013, Mr. Snowden remains a US citizen," Holder wrote.

"He is eligible for a limited validity passport good for direct return to the United States. The United States is willing to immediately issue such a passport to Mr. Snowden."

The head of a civic panel that advises the Russian migration service warned Friday that Snowden could still stay half a year in Sheremetyevo while his asylum application is considered.