* VP tells country to beware "rumor-mongers, destabilizers"
* Opposition demands more details on Chavez's condition (Adds opposition, information minister, Chavez daughter, details)
By Andrew Cawthorne
CARACAS, March 2 Ailing Venezuelan President Hugo Chavez has been undergoing "tougher" new treatment for cancer, including chemotherapy at the military hospital where he has been for the past two weeks, his vice president said.
Speaking after a Catholic Mass to pray for Chavez's health, Nicolas Maduro described how the socialist president had personally given the order to leave Cuba in mid-February, two months after his latest cancer surgery there.
"He said, 'I've taken the decision to return to Venezuela, I'm going to enter a new phase of complementary treatments, tougher and more intense, I want to be in Caracas,'" Maduro said in the comments late on Friday.
"Do you know what the complementary treatments are? They are the chemotherapies applied to patients after operations," he added outside a chapel in the Caracas military hospital.
Apart from one set of photos showing Chavez in a Havana hospital bed, he has not been seen or heard from in public since the Dec. 11 surgery in Cuba, his fourth operation since the disease was detected in mid-2011.
Chavez had previous rounds of chemo- and radiotherapy, which at times left him bald and bloated. He twice wrongly declared himself cured.
Furious at rumors swirling all week that Chavez may have died, Maduro said chemotherapy was only possible because his condition had actually improved in January after a delicate few weeks following the December operation.
Chavez's No. 2 urged Venezuelans to be on guard against "rumor-mongers" and "destabilizers," saying right-wing politicians in the United States were in league with Venezuela's opposition to spread lies about his boss.
"Sadly, the opposition live in a world of hatred, wrongdoing, bad feelings and bad desires," Maduro said, adding that Chavez had become sick from overworking.
"He neglected his own body to give our people his work, his love, his life," Maduro said, confirming Chavez was still using a tracheal tube to breathe and was communicating with family and aides through written messages and other "creative" means.
'THEY MUST SHOW HIM'
Opposition leaders have accused Maduro of lying about Chavez's condition. Several dozen anti-government students have chained themselves up in public to demand proof that the president is alive and in Venezuela.
"We challenge Nicolas Maduro to say where Hugo Chavez is. They must show him," opposition leader Pablo Medina said during a visit on Saturday to the students in Caracas.
Chavez's family and supporters are smarting at the crescendo of rumors that surfaced this week in news media and on the Internet. They have ranged from a claim by a Panamanian diplomat that Chavez's family had switched his life support off, to a Spanish newspaper report he had gone to die on an island refuge.
"Let's see, let's see, gentlemen in the laboratory, what rumors have you prepared for us today?" said Information Minister Ernesto Villegas.
Chavez's daughter, Maria Gabriela, complained about the media scrutiny of her face during the Mass on Friday night. Her somber expression was interpreted by some on Twitter as a sign her father was near death.
"I can't be happy if my father is ill ... In the next Mass, I'll have to dance and laugh," she tweeted.
Should Chavez die or step down, a vote would be held within 30 days, probably pitting Maduro against opposition leader and state governor Henrique Capriles for leadership of a nation that holds the world's biggest oil reserves. Capriles lost to Chavez in last year's election.
The stakes are also high for the region. Chavez has been the most vocal Latin American critic of Washington and financed hefty aid programs for leftist governments from Cuba to Bolivia. (Additional reporting by Mario Naranjo; Editing by Peter Cooney)