Iranian President Mahmoud Ahmadinejad was to attend Nicaraguan leader Daniel Ortega's inauguration Tuesday, during a tour of Latin American allies amid growing Western fears over Iran's nuclear ambitions.

Firebrand Venezuelan President Hugo Chavez, a key financial backer to Ortega, was also due to take part, after slamming Western imperialism with his "brother" Ahmadinejad in Venezuela on Monday.

The IAEA's confirmation Monday that Iran had begun enriching uranium in a new, underground bunker was seized upon by the United States, Britain, France and Germany as an unacceptable "violation" of UN Security Council resolutions.

But while Iran downplayed the significance of the Fordo site -- and said it was ready to resume nuclear talks with world powers that collapsed a year ago -- it continued to send tough signals to its longtime foe, the United States.

On Monday, a Revolutionary Court in Tehran sentenced an American former Marine, Amir Mirzai Hekmati, to death after convicting him of being a CIA spy.

And international concern rose over a threat by Iranian political and military officials to close the Strait of Hormuz, a major oil shipping lane, if threatened by military action or if Western sanctions halt oil exports.

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.

"They don't know what's happening. We all know it's something to laugh about," Ahmadinejad said late Monday in Venezuela.

In Latin America, Venezuela's relationship with Iran raises the deepest strategic concerns for the West, although Tehran has the strongest economic ties with Brazil, notably absent from Ahmadinejad's itinerary.

In a provocative throwback to his Cold War relations with the United States, Nicaraguan President Ortega invited Ahmadinejad as a special guest to his inauguration for a third, five-year term.

Although the former revolutionary has moderated his socialist rhetoric since governing in the 1980s, he still riles the United States, while respecting a free trade accord and receiving US aid.

Many analysts believe Ortega's relationship with Iran has so far produced little more than symbolism and rhetoric, while risking US ties.

But Ortega is riding a wave of popular support at home, after winning reelection with 62 percent of the vote in November and a super majority in Congress for his Sandinista National Liberation Front (FSLN).

His latest term saw economic growth despite the global crisis, although the country of almost six million remains the poorest in the Americas after Haiti.

Ortega counts on $500 million of annual aid from Chavez to help fund popular programs for the poor.

Chavez and Ahmadinejad were set to steal the limelight Tuesday afternoon, in a ceremony in Managua's Revolution Square.

Doubts about Ortega's reelection, which went against the constitution, and alleged flaws in the vote explained how only a small number of foreign heads of state would attend.

Ahmadinejad was due to meet President Raul Castro in Cuba Wednesday, and possibly ex-revolutionary leader Fidel Castro, before traveling to Ecuador on Thursday.