By Bradley Klapper, Associated Press: WASHINGTON - The Obama administration Monday rejected Iran's charge that a young Iranian-American man used a family trip to Iran as cover for espionage, after the Tehran government issued the first death penalty against a U.S. citizen since the Islamic Revolution 33 years ago. The U.S. suggested the decision was a political ploy.

In a case that surely will heighten tensions with Tehran, Iran charged Amir Mirzaei Hekmati with receiving special training and serving at U.S. military bases in Iraq and Afghanistan before traveling to Iran on an intelligence mission. A court convicted him of belonging to the CIA and trying to incriminate Iran for involvement in terrorism, according to a state radio report Monday.

The United States denied the accusations. The State Department called them a "complete fabrication" and White House spokesman Tommy Vietor added that "allegations that Mr. Hekmati either worked for or was sent to Iran by the CIA are false."

"The Iranian regime has a history of falsely accusing people of being spies, of eliciting forced confessions and of holding innocent Americans for political reasons," Vietor said in a statement.

The case sheds light on the legal but risky travel of U.S. citizens to Iran, common among many first-generation and second-generation Iranian-Americans but a practice largely hidden to the larger American populace. Thousands are believed to make the trip each year, though the State Department doesn't have firm figures because people must travel through third countries and most dual nationals enter the Islamic republic using Iranian passports.

But the State Department has warned that U.S.-Iranian citizens aren't necessarily any safer than others from the threat of arbitrary arrest. Spokeswoman Victoria Nuland said the U.S. has issued a series of travel warnings for Americans, with specific references to those holding both U.S. and Iranian citizenship.

"We urge Iranian-Americans to take particular care," Nuland told reporters. Because Iranian authorities don't recognize dual citizenship, they treat any such people arrested as they would other Iranians. The latest U.S. travel warning says Iranian-Americans face "the risk of being targeted" by Tehran and notes that "Iranian authorities have detained and harassed U.S. citizens of Iranian origin."

Hekmati, 28, is a former military translator who was born in Arizona and graduated from high school in Michigan. His family is of Iranian origin, and Hekmati claims dual citizenship. His father, Ali, a professor at a community college in Flint, Mich., has said his son was visiting his grandmothers in Iran.

The Marine Corps said Amir Nema Hekmati served between 2001 and 2005, including a deployment to Iraq in 2004 and a stint at the military language institute in Monterey, Calif. The Marine records do not indicate any deployment to Afghanistan. It was not clear why the middle name was listed differently.

Behnaz Hekmati, Amir's mother, said in an email to The Associated Press that she and her husband are "shocked and terrified" that their son has been sentenced to death. The verdict is "the result of a process that was neither transparent nor fair," she said.

Her son did not engage in spying, she said. "Amir is not a criminal. His very life is being exploited for political gain."

In an alleged confession broadcast on Iranian state TV last month, Hekmati said he entered the Army after finishing high school in 2001 and received military and intelligence training including serving as an intelligence analyst in Iraq. He said his key responsibility was to identify Iraqi politicians sympathetic to Americans.

He said he had also worked for the military's Defense Advanced Research Projects Agency and for Kuma Games, which he described to state TV as "a computer games company which received money from CIA to design and make special films and computer games to change the public opinion's mindset in the Middle East and distribute them among Middle East residents free of charge. The goal of Kuma Games was to convince the people of the world and Iraq that what the U.S. does in Iraq and other countries is good and acceptable."

The company's website describes it as a specialist in episodic games, in which the story line of ongoing games develops like television episodes. Several of its products are war-themed.

He also said he worked for BAE Systems, where he learned how to "use secret systems and methods for gathering information from difference places and individuals. During this period, CIA was trying to find a suitable cover-up for my important mission," according to the English-language website of Iran's state TV.

From March to August 2010, Hekmati worked for BAE Systems, said company spokesman Brian Roehrkasse. He said Hekmati left the company to take a civilian position with the U.S. government, but he had no details.

The espionage charges against Hekmati are similar to previous prosecutions against Americans who were sentenced to jail time and later freed, including an Iranian-American journalist in 2009 and three U.S. citizens detained along the Iraq border. Iranian prosecutors, however, had stressed Hekmati's links to the U.S. military in calling for capital punishment.

State Department officials said they were unaware of any previous death penalty sentence on an American in Iran.

Iran and the United States currently are locked in a period of intense hostility — a situation that augurs poorly for a quick release for Hekmati.

The Obama administration has approved new sanctions against Iran over its disputed nuclear enrichment program, specifically targeting the regime's central bank and its ability to sell petroleum abroad, though they've yet to come into force. Iran has responded with warnings to American vessels against entering the Strait of Hormuz, the strategic waterway that carries to market much of the oil pumped in the Middle East.

Having imposed the worst possible sentence immediately, Iran now could seek to drag out the case. In past cases Iran has held out the possibility of releasing American prisoners on humanitarian grounds, presumably in the hopes of gaining a counter-concession from Washington. September's release of a pair of American hikers held captive by Iran for two years is the most recent example.

President Barack Obama approved the new U.S. sanctions against Iran on Dec. 31, despite his administration's fears they could spike global oil prices or cause economic hardship on American allies in Europe and Asia that import petroleum from Iran.

The measures affect foreign financial institutions doing business with Iran's central bank by barring them from doing business in the United States. The measures would apply to foreign central banks as well for transactions related to petroleum.

But the sanctions won't take effect for six months. The president also can waive them for national security reasons or if the country in question significantly reduces its purchases of Iranian oil. The State Department says it is trying to implement the law in a way that maximizes pressure on Tehran while causing minimal disruption to the U.S. and its allies.

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Associated Press writers Lolita C. Baldor, Anne Gearan and Julie Pace contributed to this report.