* Powerful trio meet Raul Castro, check on Chavez
* Venezuelan leader still unseen since Dec. 11 operation
* Opposition demand "truth" on president's condition
By Andrew Cawthorne
CARACAS, Jan 13 (Reuters) - Venezuela's three most powerful government figures after President Hugo Chavez were again gathered in Havana on Sunday to check on their ailing leader's condition and meet with Cuban allies.
Vice-President Nicolas Maduro, Congress head Diosdado Cabello, and Oil Minister Rafael Ramirez have been shuttling to and from Cuba since the 58-year-old socialist president's fourth and most serious cancer surgery a month ago.
Chavez, who missed his own inauguration for a new, six-year term last week, has not been seen or heard from in public since the surgery. Many Venezuelans are assuming his momentous 14-year rule of the South American OPEC nation could be nearing an end.
Though acknowledging the gravity of the situation, officials are trying to stay upbeat on socialist president's prospects for recovery, and Chavez's brother on Saturday denied that Chavez was in a coma.
"We are all Chavez!" and "Chavez will return!" were among slogans sang and chanted at numerous solidarity rallies, meetings and concerts across Venezuela over the weekend drawing thousands of passionate and anxious supporters.
Information Minister Ernesto Villegas said Maduro, who Chavez recently designated as his successor, informed Venezuela's leader of the support for him back home. He gave no more details of their encounter or the president's condition.
State media said Maduro, Cabello, Ramirez - who also heads the powerful state oil company PDVSA - and Attorney General Cilia Flores all met Cuban President Raul Castro over the weekend.
But there were no details of the talks.
'TELL THE TRUTH'
The joint presence of top Venezuelan officials in Havana inevitably deepens rumors Chavez is at death's door - and draws opposition criticism that Raul and Fidel Castro are giving instructions behind the scenes.
But officials have been lashing "necrophilic" opponents for such speculation, and Chavez's brother said on Saturday that, on the contrary, he was improving daily.
One opposition leader, Julio Borges, said on Sunday the secrecy around Chavez's exact condition was unacceptable.
"No one is asking for details of the operation or the president's treatment, but that simply they tell the truth about his health prognosis," said Borges, a right-wing legislator who wants Chavez formally declared absent from office.
That would trigger the naming of a caretaker president, and an election within a month, but Venezuela's Supreme Court has ratified that Chavez remains president with Maduro in charge as No. 2 until his health situation is clarified.
"It's been a year-and-a-half of contradictions and announcements of his complete curing followed by relapses," Borges added, saying problems like inflation, housing shortages and power-cuts were being neglected during a political impasse.
Since the disease was discovered in mid-2011, Chavez has in fact wrongly declared himself cured twice, in an extraordinary and unsettling saga for Venezuela's 29 million people.
The stakes are high for the wider region too. Cuba and a handful of other leftist-ruled nations have for years been depending on Chavez's aid to bolster fragile economies.