Hugo Chavez called his leading presidential challenger a liar and urged his enemies to respect the result of Sunday's vote, saying an upset would be impossible.

Chavez lashed out at opposition candidate Manuel Rosales, who has called the vote a choice between democracy and an increasingly authoritarian system.

"There are two options here — ours and that of the U.S. empire and its flunkeys here, who were the ones who staged the coup," Chavez said, referring to the two-day putsch of 2002, when Chavez was returned to power by street protests and loyalists in the military.

Chavez spoke at a news conference on the final day of campaigning, a day after Rosales urged the government to avoid fraud.

"It has to be a clean game ... If that happens, all of us will be calm," Manuel Rosales, governor of oil-rich Zulia state, told The Associated Press shortly before closing his campaign with a huge rally in Maracaibo, Venezuela's second-largest city.

At his news conference, Chavez accused Rosales of lying about signing a document supporting the short-lived coup.

"What nerve! And a gentleman like that wants to be president!" Chavez said, adding, "A liar cannot be president of a country, much less of Venezuela."

Chavez also insisted that his proposal for constitutional changes extending possible elected presidential terms "is not a dictatorship, it's democracy." He noted that presidents of France have served long periods in power.

Venezuela has become increasingly polarized along class lines, with the wealthier supporting Rosales, the poor backing Chavez and a fractured middle class.

Shoppers are packing supermarkets to stock up on supplies, fearful that Sunday's outcome could prompt street protests and violence.

Both Rosales and Chavez have warned their supporters to be alert for fraud and to be ready to defend the vote.

The exchange of warnings came as a top lawmaker from Chavez's ruling party, Iris Varela, called on government supporters to take over private TV stations if they report that Rosales is leading. She said pro-opposition media may use rigged exit polls to falsely show a Rosales advantage.

"When they start to do that, we must take over the TV channels ... a peaceful takeover as we have always done at the doors of these TV stations," she told the state TV broadcaster in an interview, singling out two Caracas stations, Globovision and RCTV — both highly critical of the government.

Varela denied she was emitting a threat, saying, "we are only going to demand they say the truth, that's it."

Holding up a copy of the constitution, she said: "Christ died for the truth ... It's a constitutional duty — as a revolutionary, I can't stand with my arms crossed before something (that's) trying to change the popular will."

In Maracaibo, hundreds of thousands dancing to the pulse of reggaeton music packed a dozen blocks along a major road in support of Rosales, who ended his campaign with momentum on Wednesday after uniting Venezuela's opposition movement for the first time since a crushing defeat in a 2004 recall referendum against Chavez.

Rosales has accused Chavez of seeking to exploit divisions in order to consolidate power, and warns the Venezuelan leader's "socialist revolution" aims to copy Cuban President Fidel Castro's one-man communist system.

"This is not just any election. We're not deciding on a president," Rosales told the crowd. "We're going to choose between two paths — one side that believes in democracy ... and the other that wants to establish in Venezuela a Castro-Cuban communist system that strips the people of freedom."

Rosales supporters cite polls showing Sunday's race will be tight, although an independent AP-Ipsos survey and other recent polls found Chavez with a large lead.