Venezuela's President Hugo Chavez experienced "complications," including bleeding, during his cancer surgery, but is showing positive signs of recovery, senior aides say.

The health of the ailing leader, who has embodied the Latin American left for more than a decade and was re-elected in October, has been the subject of intense speculation since he was first diagnosed with cancer last year.

During his latest treatment, 58-year-old Chavez suffered "bleeding that required the adoption of corrective measures," Communications Minister Ernesto Villegas said Thursday in a television and radio address.

It was the first time Venezuelan officials had acknowledged complications in the six hours of surgery that Chavez underwent on Tuesday in Havana.

Chavez is undergoing "a progressive and favorable recovery," Villegas told the nation, warning that this "requires a precautionary time" due to the "complexity of the operation and also because of complications that arose."

Vice President Nicolas Maduro, the former foreign minister to whom Chavez bequeathed the reins of power before flying to Havana, also said that the president's condition was improving.

"In the last hours the process of recovery has evolved from stable to favorable," Maduro said, describing it as one of "progressive recovery."

Chavez aides have warned Venezuelans to be prepared for the worst as the country, already deeply divided over the firebrand leader's populist policies, heads into a period of uncertainty.

Diosdado Cabello, a senior leader of Chavez's party, urged the armed forces to stay united and be wary of any attempt to destabilize the country. He said Chavez himself had warned against dissent before flying to Cuba.

The latest turn in the 18-month-old saga comes before Chavez was scheduled to be sworn in on January 10 to another six-year term, and three days before regional elections seen as a key test of his political strength.

Before departing for Cuba on Sunday, Chavez left Maduro in charge, for the first time naming him as his successor in the event he can no longer govern.

Venezuela's constitution calls for new presidential elections to be held within 30 days if the president is incapacitated, either before he can be sworn in or during his first four years in power.

The presidential inauguration cannot be postponed in case of illness, and Chavez must be in the country when he takes the oath of office.

Procedural issues aside, there was the broader question of the political void Chavez would leave if he dies or must step aside.

Chavez has reserved for himself every major decision since taking office in 1999, dominating a highly personalized movement.

Until last week, when he stunned the nation with news that his cancer had returned, Chavez appeared to have banked on making a full recovery, despite several debilitating rounds of radiation treatment and chemotherapy.

Chavez claimed he was cancer-free before embarking on his successful but arduous reelection campaign earlier this year.

In recent days, Chavez supporters have held religious services and candlelight vigils across the country to pray for their leader, and state television has been broadcasting spots praising Chavez's accomplishments.

Henrique Capriles, the opposition candidate Chavez defeated in the October presidential election, accused the government of using the president's illness to get out the vote in Sunday's regional elections.

"What does what is happening to the president have to do with the election?" said Capriles, 40, who is running for reelection as governor of Miranda, where Caracas is located.

Maduro has repeatedly called on Venezuelans to vote for pro-Chavez candidates, and on Thursday said: "I swear by the loyalty and love for our comandante that we have to stand with those in government positions.

"We will never betray the people of Venezuela," he said.

Chavez supporters are expected to win in most of Venezuela's 23 states, but some in the opposition see his relapse as offering them a new opportunity.

"There were people who were disappointed after the presidential election, but they woke up after Chavez's relapse, because now there is a new chance to reclaim the country," said Maria Reveron, a 39-year-old Capriles supporter.

Messages of support for Chavez meanwhile poured in from leftist Latin American leaders.

"For Chavez, our brother in the struggle, we reiterate all our affection and solidarity and wish that... he emerges stronger," Cuban President Raul Castro said in his first comments since Chavez landed in Cuba for surgery.

The communist regime in Havana depends heavily on support from oil-rich Venezuela.