However, it is the severity of the sentence that is unusual and is shocking to the human rights group.

"Espionage in theory can carry the death penalty but since the revolution in 1979 this is the first time that a U.S citizen has been sentenced to death for such a charge," explained Auerbach.

Another worrying aspect of the 28-year-old former Marine's case is that unlike in America where convicted criminals can live on death row for years, Iran is not conservative when it comes to carrying out executions.

"For a number of years, Iran has been the number two executioner in the world after China and that has spiked recently," said Auerbach.

"There were at least 600 executions in 2011 and indications show that there has already been 40 in 2012, and we're only 11 days into the year."

According to his family, who live in Flint, Michigan, Hekmati traveled to Iran to visit his elderly grandmother who had been ill.

Despite declaring that he had served in the U.S. military and obtaining permission from the Iranian Interests Section of the Pakistani Embassy in Washington D.C., the businessman was arrested in August 2011 and charged with allegedly spying for the CIA.

Along with his background as a former Marine, Hekmati's business involvement in a reality-based war video game, his Iranian heritage, and linguistics work he did for the Defense Advanced Research Projects Agency, could all have contributed to why he became a target of the Iranian authorities, reported the New York Times.