CARACAS, Venezuela (CNN) -- President Hugo Chavez on Friday wrapped up his campaign to push through broad constitutional changes with a broadside attack against adversaries at home and abroad -- including a threat to cut off oil exports to the United States.

Supporters of President Hugo Chavez rally Friday in Caracas, Venezuela.

Chavez told a crowd gathered in the center of Caracas that if the referendum was approved and the result was questioned -- "if the 'yes' vote wins on Sunday and the Venezuelan oligarchy, playing the [U.S.] empire's game, comes with their little stories of fraud" -- then he would order oil shipments to the United States halted Monday.

Chavez spoke after tens of thousands, brought on buses from throughout the country, marched down the capital's principal boulevard to rally support for Sunday's referendum, which would free Chavez from term-limit restrictions and move the country toward institutionalized socialism.

Friday's rally acted as a counterpoint to an opposition march down the same streets Thursday that brought out tens of thousands who fear the 69 constitutional changes would serve to undermine basic democratic freedoms.

Chavez, 53, warmed the crowd up by serenading them with holiday "gaitas" and other traditional songs before turning his attention to a litany of enemies and perceived enemies: internal critics, the United States, Spain's King Juan Carlos, Colombia's President Alvaro Uribe and domestic and international media.

"We're not really confronting those peons of imperialism," Chavez said, alluding to his Venezuelan opponents. "Our true enemy is called the North American empire, and ... we're going to give another knockout to Bush."

He renewed his harsh criticisms of Juan Carlos and Uribe, with whom he has had recent high-profile disputes, and threatened to take independent Venezuela television network Globovision off the air if it broadcast partial results during the voting. He also threatened to take action against international networks, accusing CNN in particular of overstating the strength of the opposition's numbers.

"If any international channel comes here to take part in an operation from the imperialist against Venezuela, your reporters will be thrown out of the country, they will not be able to work here," Chavez said. "People at CNN, listen carefully: This is just a warning."

At stake in Sunday's vote is whether the leftist leader should have full authority over the now autonomous Central Bank and with it the nation's economic policy, changes Chavez has said he needs to move the economy further toward socialism.

The most controversial amendment would do away with term limits, allowing Chavez, who has served almost eight years in power, to hold his post indefinitely as long as he is re-elected.

Chavez, a former paratrooper, said the majority of the country's 26 million people back him. He has garnered overwhelming support from the country's poorer neighborhoods, who have benefited from his policies -- paid for by skyrocketing oil prices. Oil accounts for roughly 90 percent of the country's export earnings, according to the CIA World Factbook.

Despite the animosity that Chavez routinely aims at the United States, the two countries remain closely tied economically -- the United States is Venezuela's biggest oil customer and one of the few countries that can refine its low-quality crude. Venezuela accounts for up to 15 percent of U.S. crude imports. E-mail to a friend

CNN's Harris Whitbeck contributed to this report.

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