An Iranian court sentenced a Michigan man to death on espionage charges Monday, drawing an angry response from the Obama administration and driving up the temperature in an increasingly volatile feud between the two countries.

Amir Mirzaei Hekmati, a former U.S. Marine of Iranian descent, was handed a death sentence for a list of alleged crimes that included spying for the CIA, state media reported. U.S. officials said the charges were false and politically motivated, describing them as the latest in a series of provocations by Iran’s clerical rulers.

“We strongly condemn this verdict,” said Victoria Nuland, spokeswoman for the State Department.

Iranian authorities accused Hekmati, 28, of receiving special training at U.S. bases in Iraq and Afghanistan before being dispatched to Iran on a spy mission. Hekmati, who was born in Arizona and holds dual citizenship, was given 20 days to appeal the verdict.

The court’s decision comes at a time of increasing tension between Tehran and Washington, as the United States and its allies seek to dramatically toughen economic sanctions against Iran over its nuclear program.

Iran has sought to retaliate by threatening to block the Strait of Hormuz and warning a U.S. aircraft carrier not to enter the strategic waterway. Iran has also boasted in recent days of new progress in its nuclear program, signaling that it has achieved its long-stated ambition of starting uranium enrichment at a mountain bunker, using a process that makes uranium that can be upgraded for weapons use more quickly than the country’s main stockpile. The International Atomic Energy Agency confirmed the assertion Monday.

U.S. officials and Iran experts view the charges against Hekmati as further evidence that Iranian leaders are feeling pressure and are looking for ways to regain advantage. One analyst described the former Marine as “another hostage of the U.S.-Iran cold war.”

“The Iranian regime is desperate for any leverage it can get vis-a-vis the United States,” said Karim Sadjadpour, an Iran analyst with the Carnegie Endowment for International Peace. “For that reason, it’s highly unlikely that they’ll execute Mr. Hekmati, for he would then cease to be a bargaining chip.”

President Obama signed a bill on the last day of 2011 that placed the Central Bank of Iran under unilateral sanctions, setting off a steep slide in the Iranian currency. Since then, Europe has indicated that it will impose stiff sanctions of its own.

The signs of strain in Tehran have encouraged U.S. officials in their belief that Iran’s leaders will eventually come around to negotiations over their nuclear program. But Greg Thielmann, a senior fellow at the Arms Control Association, said the international action may instead be prompting Iran to become even less cooperative. “The Iranians feel a need to push back with every apparent application of pressure by the international community, for domestic political reasons and to maximize their leverage,” Thielmann, a former State Department official, said in e-mailed comments.

Precisely when and where Hekmati was arrested is unclear. Iranian news reports have said that he was detained in late August or early September, according to the Associated Press. Iranian media have also reported that Hekmati was spotted by Iranian intelligence operatives while visiting Bagram air base, 35 miles north of Kabul.

Hekmati’s family members, who live in Michigan, reportedly said that he was in Iran to visit his grandmother.

Nuland, the State Department spokeswoman, said U.S. officials were working through the Swiss Embassy in Tehran to obtain information about Hekmati’s case and to press for his release. The Swiss government represents U.S. interests in Iran because Tehran does not have diplomatic relations with Washington.

“Allegations that Mr. Hekmati either worked for or was sent to Iran by the CIA are simply untrue,” she said. “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.”

Hekmati appeared on Iranian state television in December and purportedly confessed to working for the CIA. It is unclear whether the statements were made under duress.

“It was their plan to first burn some useful information, give it to them [the Iranians] and let the Intelligence Ministry think that this is good material and contact me afterwards,” Hekmati said in his television appearance.

He went on to say that the CIA ordered him “to become a source for [Iran’s] Intelligence Ministry” and remain in Tehran “for three weeks and feed them this information, get some money for it and come back.”

The assassination of several Iranian nuclear scientists and mysterious explosions at military and industrial sites in Iran in recent years have prompted Tehran to keep closer tabs on dual nationals visiting the country. The Tehran government considers Hekmati an Iranian, not an American, because Iran does not recognize dual citizenship.

During Hekmati’s trial, the state prosecutor demanded “the most severe punishment” in retaliation for what he alleged was increased spy activities by the United States, the semiofficial Fars News Agency reported.

Hekmati was convicted of working with a hostile country, belonging to the CIA and trying to accuse Iran of involvement in terrorism, Fars reported.

The court described him as a “mohareb,” an Islamic legal term meaning that he “waged war against God,” and a “mofsed,” or someone who “spreads corruption on the earth,” the AP reported.

The judge, Abolghassem Salavati, has presided over mass trials against activists, sentencing at least three people to death after giving them similar labels.

The sentence was announced as Iranian President Mahmoud Ahmadinejad began the first leg of a four-country tour of Latin America. After arriving in the Venezuelan capital, he received a warm welcome from President Hugo Chavez, who also considers the United States an adversary. The Venezuelan populist, standing beside the Iranian leader, sharply criticized the Obama administration and its efforts to isolate Iran.

“The imperialism,” Chavez said, referring to the United States, “accuses us of being war-like. We are not. Iran has invaded no one. The Iranian Islamic revolution has invaded no one.” He said that his government’s relationship with Iran is commercial, reeling off deals with Tehran that he says have led to a range of projects, including in the housing and manufacturing sectors.

Ahmadinejad, speaking through an interpreter, cast his government as one interested only in improving people’s lives. “We are not one to attack other people,” he said. “Our bombs are love and kindness toward peoples. Our fuel is the desire of liberty and independence for the peoples. Our weapon is logic, culture, human values, love, kindness and friendship.”

Warrick reported from Washington. Correspondent Juan Forero in Bogota, Colombia, contributed to this report.