Iranian President Mahmoud Ahmadinejad was to meet Venezuelan leader Hugo Chavez on Monday to kick off a tour to rally the support of Latin American allies amid growing nuclear tensions with the West.

The UN's atomic energy watchdog confirmed earlier Monday that Iran had started enriching uranium at a new site in a difficult-to-bomb mountain bunker, in a move set to further heighten international concerns.

As Ahmadinejad began his five-day tour of regional allies Venezuela, Nicaragua, Cuba and Ecuador, Iran also ratcheted up tensions with the United States by sentencing to death an American arrested as a spy.

Ahmadinejad made no comment as he arrived Sunday in Caracas.

Washington last week told the Latin American nations that it was not "the moment" to deepen ties with Iran.

Firebrand Chavez, a fellow US foe, laughed off the warning. He was due to meet Ahmadinejad at 1830 GMT in the Miraflores presidential palace in Caracas.

The Iranian leader is under increasing pressure from the United States and the European Union to abandon the country's nuclear program, which Western nations suspect seeks to develop an atomic bomb, despite Iran's denials.

Iran's supreme leader Ayatollah Ali Khamenei said Monday that the Islamic republic would "resist the pressures" of Western powers.

Iranian political and military officials have threatened to close the Strait of Hormuz, the world's most important oil shipping lane, if threatened by military action or if sanctions halt oil exports.

In Latin America it is Venezuela's relationship with Iran that raises the deepest strategic and political concerns for the West, although Tehran has the strongest economic ties with Brazil.

Observers wonder how much leftist Chavez might undermine international sanctions against Iran by providing fuel or cash to Islamic Republic.

"We'll see how the Chavez government moves tactically today (Monday) and how he'll support Iran," said Venezuelan analyst Elsa Cardozo, from the Metropolitan University of Caracas.

"It's possible that he'll share very radical and confrontational decisions with Ahmadinejad, but he could also suggest mediation, projecting a more conciliatory image, which would suit the leadership role he wants to take in Latin America."

Ahmadinejad's arrival in Caracas also coincided with Washington's announcement to expel the Venezuelan consul in Miami.

Livia Acosta Noguera was accused in a documentary on Spanish-language channel Univision of links to a suspect Iranian plot against US nuclear installations.

Chavez has not yet commented on the US move but could take some kind of retaliatory measure, according to analysts.

Venezuela and Iran, which both belong to OPEC, have economic ties of around $5 billion as well as a string of deals from building low income homes to bicycles in Venezuela, most of which have yet to start.

Ahmadinejad, who is traveling with his foreign minister and economy and energy ministers, last visited Venezuela in November 2009.

He was due to travel Tuesday to Nicaragua to take part in the inauguration ceremony following President Daniel Ortega's reelection before traveling to Cuba and Ecuador.

The International Atomic Energy Agency confirmed Monday that Iran has started enriching uranium to 20-percent purity at a reinforced facility sunk deep under a mountain at Fordo, 150 kilometers (90 miles) southwest of Tehran.

The United States meanwhile condemned the death sentence handed to US-Iranian ex-Marine Amir Mirza Hekmati in Iran and said allegations that he worked for the CIA were "false."