Venezuela's government scoffed on Tuesday at a report that Hugo Chavez is in Cuba for more urgent cancer treatment, denouncing it as part of a dirty war by the opposition ahead of a presidential election in October.

It was just the latest in a cycle of rumours about the health of the socialist leader that have ranged all the way from him having only months left to live to the whole saga being a pre-vote invention by his allies to let him make a Messiah-like return.

A prominent opposition-leaning Venezuelan journalist, Nelson Bocaranda, wrote on Monday that Chavez, who had surgery in Havana last June to remove a tumour from his pelvis, had returned to Cuba and that some of his relatives were flying there too.

But the government denied it, with Information Minister Andres Izarra saying it was rumor spread as part of a dirty war by scum, while Congress leader Diosdado Cabello said Chavez was healthy and could give his detractors a surprise on Tuesday.

Bocaranda is sick in his soul. Every day he wishes for the death of the commandante, or is it that someone is paying him to write his lies? Cabello wrote on Twitter.

The rumours spread particularly fast during a four-day Carnival weekend in Venezuela, when official business all but halts as most people head to the beach or to visit relatives.

Last year, Bocaranda broke news about Chavez's cancer treatment on the communist-led Caribbean island. Since then, the 57-year-old president has insisted he is completely recovered, although medical experts say it is too soon to make such a call.

Chavez's health is the wildcard in the run-up to the October 7 election when he will seek a new six-year term. The opposition are newly united behind one candidate - Henrique Capriles - and see the vote as their best chance to end Chavez's 13 years in power.

Recent opinion polls have given Chavez an edge over Capriles, thanks partly to a huge program of new state spending on social projects. But about a third of Venezuelans remain undecided, and competition for their votes will be intense.

IGNORING HIS DOCTORS?

One medical source close to the team treating Chavez in Venezuela told Reuters he was suffering a tumour lysis, or cell breakdown, which presented itself with symptoms including a high fever. But the source did not know if he had returned to Cuba.

Bocaranda said the president's recent health problems were exacerbated by him ignoring his doctors' orders to get enough rest because he wanted to get back on the campaign trail and confront Capriles. And, he added that they had warned him of the damage he was doing to himself through the heavy use of steroids to look healthy in public.

The last time Chavez made an appearance was at a February 16 graduation ceremony for medical students when he gave a long televised speech in which he called Capriles a low-life pig.

Venezuelan analyst Diego Moya-Ocampos at IHS Global Insight said that whether or not the rumours were true, the fact they spread so fast underlined the anxiety among supporters each time Chavez vanished from view for more than a couple of days.

But Moya-Ocampos said it was important to note that the president had squashed all such rumours in the past by appearing on state TV to deliver more of his signature marathon speeches.

Chavez's absence could well be a strategy developed by his campaign team to centre the attention back on him rather than on Capriles, who, since winning the opposition primaries, has been at the centre of media and political attention, he said.

Russ Dallen, head trader at Caracas-based BBO Financial Services, said the latest health rumor had supported Venezuela's widely traded bonds among investors hoping for regime change and a victory by the more business-friendly Capriles in October.

(Additional reporting by Marianna Parraga; Editing by Jackie Frank)