The U.S. government has strongly denied Chavez's claims that it is considering military action against Cuba's closest ally in the Americas.

But Chavez said late Monday that the U.S. government, which "won't stop caressing the idea of invading Cuba or invading Venezuela," should be warned of the consequences.

"If someday they get the crazy idea of coming to invade us, we'll make them bite the dust defending the freedom of our land," Chavez said to applause.

He spoke during the opening ceremony of a world youth festival bringing together student delegations from across the world and convened under the slogan "Against Imperialism and War."

Chavez called the United States the "most savage, cruel and murderous empire that has existed in the history of the world."

The Venezuelan leader said "socialism is the only path," and told the students the collective goal is to "save a world threatened by the voracity of U.S. imperialism."

Earlier, the students waved flags, danced in traditional dress, and held signs praising socialism, Cuban leader Fidel Castro and Ernesto "Che" Guevara.

More than 300 students from the United States shouted out their disapproval of U.S. President George W. Bush, chanting "Get out Bush!" Other students chanted: "Bush, fascist -- you're a terrorist!"

Some 15,000 youths from 144 countries traveled to Venezuela for the weeklong festival and conference, organizers said.

Chavez wore a red shirt like many of the students, and embraced delegation leaders as their groups marched past.

The ceremony was held in Venezuela's military headquarters in Caracas. Troops looked on while students passed carrying colored flags and shouting: "We will overcome!"

This year's World Festival of Students and Youth is the 16th. The first, in 1947, was held in Czechoslovakia, and during the Cold War most host countries were aligned with the Soviet bloc.

Apart from the former Soviet Union, other host countries have included Romania, Poland, Finland, Cuba, the former East Germany and North Korea.

The weeklong gathering will include musical performances, panel discussions and an "Anti-imperialist Court," which in past years has condemned the U.S. government's actions.

While tensions have grown between Chavez and Washington, the Venezuelan leader has built close ties with countries from Iran to China.

Chavez expressed his support Monday for Iran's new president, Mahmoud Ahmadinejad, saying he expects to continue strengthening relations. Chavez said like Venezuela, Iran is a country that has been "attacked" for many years by "the hand of imperialism."

Chavez, whose country remains a major supplier of oil to the United States, also is sharply critical of the U.S.-led wars in Afghanistan and Iraq.