CARACAS, Venezuela (CNN) -- A Colombian rebel group holding hostages had agreed to release some of them by the end of the year, but Colombian President Alvaro Uribe has derailed those plans, Venezuelan President Hugo Chavez told reporters Saturday.
Venezuelan President Hugo Chavez delivers a speech during a news conference in Caracas Saturday.
Chavez, who has been mediating with the rebels, said a commander of the Revolutionary Armed Forces of Colombia (FARC) had agreed to release the first group by Christmas.
The captives include a Colombian senator and three American contractors.
At a wide-ranging news conference in Caracas, Chavez accused Uribe of being a liar and accused the Colombian government of working with the United States -- another frequent Chavez target -- to block the hostages' release.
The 53-year-old Venezuelan president was barred by election rules from discussing Sunday's referendum on constitutional changes that would abolish presidential term limits and move the country toward institutionalized socialism.
He said Friday that if the referendum passes and "the Venezuelan oligarchy, playing the [U.S.] empire's game, comes with their little stories of fraud," then he will order oil shipments to the United States halted first thing Monday.
He expanded that threat Saturday, saying he would halt oil exports worldwide if Venezuela is invaded or if attempts are made to oust him.
Chavez used much of the news conference for foreign reporters to criticize the media, singling out CNN in particular.
He pointed to an on-screen caption on its Spanish-language network earlier this week that he said was an incitement to assassinate him.
On Tuesday, CNN en Espanol showed a picture of Chavez with a caption saying, "Who killed him?" at the bottom of the screen. The caption was meant to be used on a story about Washington Redskins football player Sean Taylor, who was killed last Monday. CNN has apologized for the error.
In a statement responding to Chavez's comments, CNN said, "We are committed to continuing to cover the current situation in Venezuela in a fair and objective manner. For example, we've frequently offered live, extended coverage of President Chavez's speeches and news conferences, even when he uses our air to voice his criticisms of CNN."
Chavez has threatened to sue the network and expel CNN employees from the country. Watch Chavez criticize CNN »
Asked about his attitude toward CNN by its reporter Patricia Janiot, Chavez said, "I think it's the channel that I watch the most, CNN. There isn't any day I don't turn it on at dawn to see what's going on. It's irrefutable, I am addicted."
But, he said, "CNN is a tyranny ... it is the CNN owners' fault. A tyranny."
Chavez's relationship with CNN -- and the media in general -- has been rocky.
In May, the Venezuelan government opened an investigation into broadcasters it claimed were inciting the public to violence over its decision not to renew the broadcast license of RCTV, an opposition television station that had been broadcasting for 53 years.
On Friday, Chavez threatened to take independent Venezuelan network Globovision off the air if it broadcast partial results of a Sunday referendum during the voting.
Chavez, a former paratrooper, insists the majority of the country's 26 million people back him. He enjoys widespread support in poorer neighborhoods, which have benefited from his policies -- paid for by skyrocketing oil prices. Oil accounts for roughly 90 percent of Venezuela's export earnings.
Despite the animosity that Chavez displays toward 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 is one of the top five sources of oil for the United States, which imports about a million barrels of Venezuelan oil daily. E-mail to a friend
CNN's Harris Whitbeck contributed to this report.