CARACAS (Reuters) - Venezuelan President Hugo Chavez said on Friday he was preparing for a second round of chemotherapy treatment in Cuba to eliminate the risk of malignant cells.

The announcement by the 56-year-old socialist leader that he had surgery inHavana last month to remove a baseball-sized tumor has called into question his fitness to run for re-election next year in the OPEC nation of 29 million people.

Last weekend, Chavez flew back to Cuba for chemotherapy after delegating limited powers to his finance minister and vice president.

"I have completed the first cycle of chemotherapy treatment ... this cycle was completed successfully," he said in a phone call to a televised meeting of his ruling Socialist Party.

"We are preparing for a second cycle ... to totally defeat and eliminate any risk of the presence of malignant cells."

The finance minister said this week he had "no doubt" Chavez would be a candidate at next year's presidential poll.

Parliamentary elections last September showed the South American country split down the middle between Chavez supporters and opponents. Now, a fractious opposition coalition senses a chance to unseat a convalescing Chavez in 2012.

(Reporting by Caracas newsroom; Writing by Brian Ellsworth and Daniel Wallis)