Iranian President Mahmoud Ahmadinejad began a four-nation Latin American tour Sunday, aiming to show off relationships with allies as tensions grow over Iran's nuclear program, on the same day Iran's state radio says an American man convicted of working for the CIA has been sentenced to death.

It is the Iranian leader's fifth visit to Venezuela. He will also travel to Nicaragua, Cuba and Ecuador.

Tensions have been rising in the Mideast as Iran has warned it could retaliate against newly tightened U.S. sanctions by blocking shipping lanes out of the Persian Gulf. A large share of the world's oil tanker traffic passes through the Strait of Hormuz.

What the empire does is make you laugh, in its desperation to do something they won't be able to do: dominate this world.

- Hugo Chávez, President of Venezuela

Ahmadinejad smiled and waved but made no comments as he stepped off a plane Sunday evening at Simon Bolivar International Airport near Caracas. He was greeted by Vice President Elias Jaua and other Venezuelan officials.

The Iranian leader was scheduled to meet Monday with his longtime ally President Hugo Chávez, who was on a trip in eastern Venezuela on Sunday.

The visit comes on the same day an Iranian state radio reports that a former U.S. Marine, Amir Mirzaei Hekmati, was sentenced to death for spying for the U.S.. The report says Hekmati received special training and served at U.S. military bases in Iraq and Afghanistan before heading to Iran for his alleged intelligence mission. The radio report did not say when the verdict was issued. Under Iranian law, he has 20 days to appeal.

The 28-year-old former military translator was born in Arizona and graduated from high school in Michigan. His family is of Iranian origin. His father, a professor at a community college in Flint, Michigan, has said his son is not a CIA spy and was visiting his grandmothers in Iran when he was arrested.

His trial took place as the U.S. announced new, tougher sanctions against Iran over its nuclear program, which Washington believes Tehran is using to develop a possible atomic weapons capability.

Iran, which says it only seeks nuclear reactors for energy and research, has sharply increased its threats and military posturing against stronger pressures, including the U.S. sanctions targeting Iran's Central Bank in attempts to complicate its ability to sell oil.

The U.S. State Department has demanded Hekmati's release.

Hekmati's father, Ali, said in a December interview with The Associated Press, that his son was a former Arabic translator in the U.S. Marines who entered Iran about four months earlier to visit his grandmothers.

Meanwhile, several hours before Ahmadinejad's arrival on Sunday, Chávez rebuffed calls by U.S. officials for countries to insist that Iran stop defying international efforts to assess its nuclear program.

"What the empire does is make you laugh, in its desperation to do something they won't be able to do: dominate this world," Chávez said.

The U.S. and its allies accuse Iran of trying to develop nuclear weapons under the cover of a civilian nuclear energy program. France has been pressing the European Union to impose additional sanctions.

Chávez and his allies in the left-leaning Bolivarian Alliance, or ALBA bloc, have backed Iran in the dispute.

Chávez praised Iran's military industry, noting that it has long-range missiles.

He suggested that is a major reason why the U.S. "empire is trying to put the brakes on them, using as an excuse the development of nuclear energy for peaceful purposes."

He also dismissed speculation by some officials in Washington that Iran might eventually be able to use Latin American countries to stage attacks on U.S. interests.

"That must be looked at carefully because it's a threat against us," Chávez said. "We aren't a threat to anyone. We just have rights and we're sovereign."

Ahmadinejad and Chávez both plan to travel to Nicaragua for Tuesday's inauguration of newly re-elected President Daniel Ortega.

Based on reporting by the Associated Press.

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