Venezuela and Iran railed against Western imperialism Monday as Iranian President Mahmoud Ahmadinejad began a tour of Latin America amid mounting tensions over Tehran's suspect nuclear program.

As the Iranian leader met with firebrand Venezuelan President Hugo Chavez in Caracas, the UN's atomic energy watchdog confirmed that Iran had started enriching uranium at a new site in a difficult-to-bomb mountain bunker, in a move set to stoke Western suspicions that Tehran wants atomic weapons.

Iran also ratcheted up tensions with the United States by sentencing to death a US-Iranian man for allegedly spying for the CIA, a move quickly condemned by Washington.

Chavez and Ahmadinejad, who have strengthened ties in recent years and intensified their hostility towards Washington, greeted each other as "brothers" before a meeting to study bilateral deals.

"There's a desire for our governments to keep working together... to slow down the imperialist madness that has now been unleashed more than ever," Chavez said outside the Miraflores presidential palace.

"The Venezuelan and Iranian people are on the way to fighting all the greed and arrogance of imperialism," Ahmadinejad said.

The Iranian leader is under increasing pressure from the United States and the European Union to abandon his country's suspect nuclear program, which Tehran insists exists solely for peaceful purposes.

Iranian political and military officials have meanwhile threatened to close the Strait of Hormuz, a major oil shipping lane, if threatened by military action or if Western sanctions halt oil exports.

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

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

"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," said Venezuelan analyst Elsa Cardozo, from the Metropolitan University of Caracas.

Ahmadinejad's arrival in Caracas came as Washington announced that the Venezuelan consul in Miami had been expelled.

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

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

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

He was due to travel Tuesday to Nicaragua to attend the inauguration ceremony for President Daniel Ortega, before traveling to Cuba and Ecuador.

In Washington, State Department spokeswoman Victoria Nuland said the United States was "calling on all of these countries to do what they can to impress upon the Iranian regime that the course that it's on in its nuclear dialogue with the international community is the wrong one."

"We think it's in the interest of all countries, including the countries that he's visiting in Latin America, that Iran proves the peaceful intent of its nuclear program to the world," Nuland said.