The US has told the Russian government that it will not seek the death penalty for Edward Snowden should he be extradited, in an attempt to prevent Moscow from granting asylum to the former National Security Agency contractor.

In a letter sent this week, US attorney general Eric Holder told his Russian counterpart that the charges faced by Snowden do not carry the death penalty. Holder added that the US "would not seek the death penalty even if Mr Snowden were charged with additional, death penalty-eligible crimes".

Holder said he had sent the letter, addressed to Alexander Vladimirovich, Russia's minister of justice, in response to reports that Snowden had applied for 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".

"These claims are entirely without merit," Holder said. In addition to his assurance that Snowden would not face capital punishment, the attorney general wrote: "Torture is unlawful in the United States."

In the letter, released by the US Department of Justice on Friday, Holder added: "We believe that 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."

The US has been seeking Snowden's extradition to face felony charges for leaking details of NSA surveillance programmes. There were authoritative reports on Wednesday that authorities in Moscow had granted Snowden permission to stay in Russia temporarily, but when Snowden's lawyer, Anatoly Kucherena, arrived to meet his client at Sheremetyevo airport, he said the papers were not yet ready.

Kucherena, who has close links to the Kremlin, said Snowden would stay in the airport's transit zone, where he has been in limbo since arriving from Hong Kong on 23 June, for the near future.

The letter from Holder, and the apparent glitch in Snowden's asylum application, suggest that Snowden's fate is far from secure.

But a spokesman for President Vladimir Putin insisted Russia has not budged from its refusal to extradite Snowden. Asked by a reporter on Friday whether the government's position had changed, Dmitry Peskov told Russian news agencies that "Russia has never extradited anyone and never will." Putin has previously insisted Russia will not extradite Snowden to the US. There is no US-Russia extradition treaty.

Putin's statement still leaves the Russian authorities room for manoeuvre, however, as Snowden is not technically on Russian soil.

Peskov said that Putin is not involved in reviewing Snowden's application or involved in discussions about the whistleblower's future with the US, though he said the Russian security service, the FSB, had been in touch with the FBI.

Speaking on Wednesday, Snowden's lawyer said he was hoped to settle in Russia. "[Snowden] wants to find work in Russia, travel and somehow create a life for himself," Kucherena told the television station Rossiya 24. He said Snowden had already begun learning Russian.

There is support among some Russian politicians for Snowden to be allowed to stay in the country. The speaker of the Russian parliament, Sergei Naryshkin, has said Snowden should be granted asylum to protect him from the death penalty.

The letter from Holder was designed to allay those fears and negate the grounds for which Snowden as allegedly applied for asylum in Russia. The attorney general said that if Snowden returned to the US he would "promptly be brought before a civilian court" and would receive "all the protections that United States law provides".

"Any questioning of Mr Snowden could be conducted only with his consent: his participation would be entirely voluntary, and his legal counsel would be present should he wish it," Holder said.

He added that despite Snowden's passport being revoked he "remains a US citizen" and said the US would facilitate a direct return to the country.

Germany's president, who helped expose the workings of East Germany's Stasi secret police, waded into the row on Friday. President Joachim Gauck, whose role is largely symbolic, said whistleblowers such as Snowden deserved respect for defending freedom.

"The fear that our telephones or mails are recorded and stored by foreign intelligence services is a constraint on the feeling of freedom and then the danger grows that freedom itself is damaged," Gauck said.