Chavez has warned of numerous alleged plots, though in recent months he has not mentioned any specific report of a conspiracy.

If he wins another six-year term in the December election, Chavez said he plans to call a referendum halfway through the term on whether he should stay on and whether a constitutional prohibition on running for subsequent terms should be eliminated.

The Venezuelan leader's four-nation tour was the latest in a series of international stops coinciding with his country's push for a rotating Security Council seat despite U.S. opposition.

"Support for Venezuela's candidacy to the U.N. Security Council has only grown. Everyday we have more of the world's support to defeat U.S. imperialism in the United Nations,'' Chavez told the cheering crowd. "For the first time in history, Venezuela truly holds a privileged, respected place in the world because we - for the first time - have a foreign policy that doesn't depend on any world power center.''

Washington is lobbying against Venezuela's bid and is backing Guatemala. The race will be decided by the General Assembly in a secret ballot in October.

The Security Council has five permanent members with veto power - the United States, Britain, Russia, China and France - and 10 rotating non-permanent members which serve two-year terms.

Chavez, first elected in 1998, has maintained loyal support partly through oil-funded social programs popular among the poor.

It was the first time in Mexican history that opposition legislators have blocked the president's annual address and marked an escalation of a crisis that has rocked the country since a bitterly contested July 2 presidential election.

"Faced with the attitude of a group of legislators that makes it impossible to read the speech I have prepared for this occasion, I am leaving the building," Fox said in the lobby of Congress before walking out.

In a televised address to the nation later on Friday, Fox said the protest that silenced him was "not an affront to me personally but to the office of the president and the Mexican people."

In the streets outside Congress, small groups of left-wing protesters threw rocks and bottles at lines of riot police but there were no serious clashes.

Lopez Obrador has led supporters in huge street protests in the last two months and his Party of the Democratic Revolution had vowed to deny Fox a platform in Congress on Friday.

They accuse the president of complicity in a massive fraud to give victory to conservative ruling party candidate Felipe Calderon, his former energy minister. But foreign observers and Mexico's top electoral court do not agree the election was rigged.

Fox was hailed as a democracy hero when he was elected in 2000, ending 71 years of one-party rule, and still enjoys high popularity ratings as he nears the end of his term.