CARACAS (Reuters) - Vice President Nicolas Maduro said unidentified groups had entered Venezuela with the aim of assassinating him and the head of the National Assembly as President Hugo Chavez recovers from cancer in Cuba.

Maduro provided no proof of the claim, which he made at a rally to mark the end of a dictatorship in the OPEC nation 55 years ago. He said he and the energy minister would travel to Havana on Wednesday to see Chavez.

"For several weeks we've been following groups that have infiltrated the country with the aim of making attempts on the life of (Assembly head) Diosdado Cabello and my own," the vice president told a crowd of red-shirted "Chavista" supporters.

"They will not manage it against either of us!" he said.

Chavez named Maduro as his preferred successor before traveling to Cuba for cancer surgery in early December, his fourth operation in 18 months for an undisclosed form of cancer in his pelvis.

The 58-year-old president's fragile health has raised the specter of political instability in the deeply polarized South American country of 29 million.

During his 14 years in power, Chavez has repeatedly accused Venezuela's "traitorous" opposition leaders of plotting to kill him but rarely offered proof.

The opposition says the charges are a smokescreen to distract from daily problems such a shortages of staple goods, sky-high inflation and one of the worst crime rates in the world.

"Now Maduro comes with the little story that we want to see an attempt against his life and that of Al Capone," opposition leader Henrique Capriles said on Twitter, referring to Cabello as the Prohibition-era U.S. gangster. "Absolute nonsense."

(Reporting by Deisy Buitrago and Daniel Wallis; Editing by Cynthia Osterman)