By Anthony Boadle and Andrew Cawthorne
BRASILIA/CARACAS (Reuters) - Venezuelan President Hugo Chavez looked set to miss a regional trade summit in Brazil on Friday, officials said, an absence bound to heighten speculation over the leftist leader's health.
Before he went to Cuba last week for more cancer-related treatment, Chavez had enthused about attending the Mercosur bloc's meeting in Brasilia to celebrate Venezuela's entry.
He has not been seen in public since November 15.
"It looks like he is not coming, but the Venezuelans have not yet confirmed that," Brazilian foreign ministry spokesman Tovar da Silva Nunes said. Another Brazilian government source said Chavez's logistics and security advance staff were leaving Brasilia.
In Caracas, a source at the Miraflores presidential palace also said Chavez, 58, was not going to travel.
The recently re-elected president traveled to Cuba nine days ago for "hyperbaric oxygenation" treatment - normally used to treat bone decay caused by radiation therapy.
Chavez has had three cancer surgeries in Cuba since mid-2011. So even though officials were portraying the latest treatment as normal follow-up after radiation, rumors are rampant that it could be more serious.
"If Chavez does not show up at the first meeting where Venezuela is a full member of Mercosur, it will create a lot of distrust over his health," said Marcelo Coutinho, professor of international relations at Rio de Janeiro's Federal University.
Officials have given no detailed information about the condition of Chavez.
He is guaranteed warm and discreet treatment in Cuba because of his friendship with past and present rulers Fidel and Raul Castro, plus the strict controls on information there.
Chavez's presence in Cuba, where he has spent more than three months in total since his first 2011 diagnosis of cancer in the pelvic region, has overshadowed December 16 regional elections in Venezuela.
Without his presence on the campaign trail, the campaign for 23 governorships has been a low-key one, failing to light up the public like October's presidential election did with a record voter turnout of more than 80 percent.
SPECULATION AND SCENARIOS
Although Chavez continues to sign decrees and make appointments from Cuba, analysts say his absence may delay decisions on some major issues like a possible devaluation of the Bolivar currency or an amnesty for jailed opponents.
Venezuelan officials have lambasted media and others for behaving like "vampires" with speculation over Chavez's condition. One pro-opposition journalist said he was using a wheelchair.
Venezuela's widely traded bonds have rallied since his departure, on investor hopes for a change to a more business-friendly government.
Newly appointed Vice President Nicolas Maduro, 49 - a former bus driver and union leader - has assumed a more prominent position amid speculation among Venezuelans over who could replace Chavez should he leave office.
Maduro, who is also foreign minister, was due to represent Venezuela at the Mercosur meeting in Brazil.
Congress head Diosdado Cabello, a former military comrade of Chavez, is also often touted as a possible successor to lead the ruling Socialist Party.
Under the constitution, an election would have to be held if Chavez were to leave office within the first four years of his new six-year term, which starts on January 10.
That would give a fresh chance to the opposition, which garnered 44 percent of the vote - and a record number of 6.5 million votes - in the October presidential poll.
An internal U.N. report drew three possible scenarios.
"If Chavez lives, his term will continue to face monumental political, economic and security challenges. If Chavez accepts his mortality and organizes a managed transition, a unified United Socialist Party of Venezuela would likely fare well in a snap election," according to the report, seen by Reuters.
"If Chavez dies unexpectedly without a clear successor, a unified opposition - likely behind former presidential candidate Henrique Capriles Radonski - would stand its best chance to come to power in over a decade."
(Additional reporting by Anthony Boadle and Esteban Israel in Brasilia, and Deisy Buitrago in Caracas; Editing by Doina Chiacu)