Snowden 'won't face death penalty'
Mr Holder said the criminal charges Snowden now faces in America do not carry the death penalty and the US will not seek his execution even if he is charged with additional serious crimes.
The reassurance, in a letter dated Tuesday, followed reports that Snowden, who leaked details of top secret US surveillance programmes, had filed papers seeking temporary asylum in Russia on grounds that if he were returned to the US he would be tortured and would face the death penalty.
Snowden has been charged with three offences in the US, including espionage, and could face up to 30 years in prison if convicted.
The attorney general's letter was sent to Alexander Vladimirovich Konovalov, the Russian minister of justice.
When Mr Snowden arrived at Moscow's international airport a month ago, he was believed to be planning simply to transfer to a flight to Cuba and then to Venezuela to seek asylum. But the US cancelled his passport, leaving him stranded.
Besides applying for temporary asylum in Russia, Snowden has said he would like to visit the countries that offered him permanent asylum - Venezuela, Bolivia and Nicaragua.
Some Russian politicians, including parliament speaker Sergei Naryshkin, have said Snowden should be granted asylum to protect him from the death penalty.
Bruce Fein, a lawyer representing Snowden's father, criticised Mr Holder.
He said: "Today the attorney general stated - apparently thinking he was being conciliatory - that if Edward Snowden were returned to the United States we wouldn't kill him or torture him. Those are concessions only in the mind of someone who's very biased."