Story highlights Parliament will convene special session over Chavez's trip to Cuba, an official says

"An operation like this, an illness like this, always carries risk," says Hugo Chavez

He says his vice president should succeed him if his health worsens

Chavez, who won reelection this year, will return to Cuba for the operation

Venezuelan President Hugo Chavez announced late Saturday that his cancer has returned and that he will go to Cuba to undergo surgery.

Speaking during a televised address from the presidential palace, he said that if his health were to worsen, Vice President Nicolas Maduro should replace him

It was the first time Chavez spoke publicly about the possibility of a successor -- a shocking admission from a man who looms larger than life in Venezuela and in Latin American politics.

"It's absolutely necessary, absolutely vital that I undergo a new operation," said Chavez.

As he spoke, he repeatedly kissed a cross and at one point broke out into song.

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"An operation like this, an illness like this, always carries risk," he said. "If something were to happen that would incapacitate me, Nicholas Maduro should not only finish my term as the constitution requires ... You should also elect Nicholas Maduro to be president."

A special session of parliament will be convened Sunday morning to consider Chavez's health and his pending trip to Cuba, Diosdado Cabello, president of the Venezuelan National Assembly, said on state-run TV.

The parliament is required under the constitution to approve any trip that takes the president out of the country for more than five days.

Just this week, Chavez returned from Cuba after receiving medical treatment. He said doctors detected malignant cells and that he expects to undergo surgery in the coming days.

The president has repeatedly spoken publicly about his cancer battle, but has never specified what type he has.

Chavez, who had surgery in 2011 to remove a cancerous tumor, has undergone further operations and radiation therapy in Cuba since then. He declared himself cancer-free in July.

The government has released few specifics, fueling widespread speculation about his health and political future.

Health rumors dogged Chavez on the campaign trail this year, but didn't stop him from winning reelection in October.

Details of his health, however, have been a closely held secret, and some people who claim to have insider knowledge say the president is in much worse condition than he publicly lets on.