Updated

Venezuela's President Hugo Chavez warned at a conference in London on Sunday that a U.S. attack on Iran would trigger an enormous military escalation, and he criticized the war in Iraq, calling it the "Vietnam of the 21st century."

Speaking to an audience of left-leaning British lawmakers and trade union representatives, Chavez said a U.S. military strike on Iran would provoke an Iranian attack on U.S. ally Israel, triggering a wider conflict in the region.

"If they attack Iran I think it will be far worse than it was in Iraq," the firebrand leader told a packed conference center. "The United States doesn't know what it's doing in Iraq: There's no government and there's civil war. Iraq is a Vietnam of the 21st century."

U.S. officials say they prefer a negotiated solution to the standoff over Iran's nuclear program, which Washington believes is aimed at developing atomic weapons. However, the Bush administration says it does not rule out the use of military force as a last resort.

Chavez, who is on a two-day visit to London aimed at energizing Europe's social movements, told the audience that an attack on Iran would also cause a spike in oil prices.

"Among other things my English friends should park their cars, because the price of oil is going to skyrocket," he said.

The gathering, organized by London Mayor Ken Livingstone, a vocal Chavez supporter, was the first event during a packed two-day schedule that includes a meeting with the city's maverick mayor and a lecture at an institute promoting cultural and commercial ties between Britain and Latin America.

Chavez will not meet with Prime Minister Tony Blair or any senior British government officials during his visit, which one political analyst pointed to as a sign of the tensions between the two governments.

Chavez's visit seemed aimed primarily at rallying support from social activists in Europe.

On Saturday, the Venezuelan leader announced at a gathering of non-governmental groups and social movements in Vienna, Austria, that he wants to provide cheap heating oil for low-income Europeans in a deal similar to one he worked out this past winter to help needy Americans.

"I'd like to do the same here in Europe," he said Saturday, without giving details about which countries could benefit from the proposal. He said Venezuelan ambassadors in Europe were looking into the matter.

Chavez's London visit drew attention to the strains in relations between his government and British leaders.

Chavez, a fierce critic of the war in Iraq, has characterized Blair as a "pawn of imperialism" over his close alliance with U.S President George W. Bush, whom Chavez has compared to Adolf Hitler.

Chavez's moves to exert greater control over his country's vast petroleum reserves have also drawn criticism from Britain and other countries.

Venezuela's London embassy, in a statement issued ahead of his trip, confirmed that Chavez would not have any contact with the British government during his stay. The statement did not mention the recent tensions, saying only that Chavez has "already had an official visit to the United Kingdom where he met with the prime minister and other British authorities."

Officials in Blair's office and the Foreign Ministry have declined to comment on the reasons why Chavez is not meeting with any senior British official, saying only that the Venezuelan leader's visit is "private."

CountryWatch: Venezuela

A researcher at the Chatham House think tank in London said that if everything was fine between the two countries, Chavez would at least meet with a senior British official.

"It's certainly a sign of quite a frictional situation between two countries," Sam Hardy said. "Chavez is going to be in London for two days," he added. It seems "that he should meet with a high-ranking official."

On Monday, Chavez attends meetings with British trade union officials before a news conference at London's City Hall. Chavez is also due to have lunch with Livingstone and guests including Harold Pinter, the Nobel Prize winning playwright, and actress and activist Bianca Jagger.

Chavez gives a lecture Monday evening at Canning House, an institution that works to strengthen commercial and cultural ties between Britain, Latin America and the Iberian Peninsula.