CARACAS (AFP) - Venezuelan leader Hugo Chavez's allies staged a show of unity on Saturday, re-electing the ruling party's Diosdado Cabello as parliamentary speaker, while their president battles cancer in Cuba.

The closing of ranks by the United Socialist Party of Venezuela (PSUV) came as it emerged as all but certain that illness will keep Mr Chavez from being sworn in to a new six-year term on Thursday as scheduled.

"The president will continue being president beyond January 10, nobody should have any doubt about that," said Mr Cabello after his election, accusing the opposition of fomenting a "coup d'etat."

Vice-President Nicolas Maduro, for his part, called the swearing-in a "formality" and said he too would stay on in office without taking any oath until there was an opportunity to do so.

Mr Cabello's re-election was intended in part to answer persistent rumors of a power struggle within the regime in Mr Chavez's more than three-week absence, the longest stretch in his 14-year presidency.

"We will never defraud the people and we will get on our knees to defend the proposal made by comandante Chavez, I swear it," Mr Cabello said as he took the oath of office.

Mr Chavez's health was invoked by both Chavistas and members of the opposition, who criticised the ruling party for refusing to engage in inclusive dialogue as the oil-rich country enters a period of high uncertainty.

"It is not only the head of state who is sick, the Republic is sick," said opposition deputy Hiran Gaviria.

"The public finances are exhausted, there are shortages, inflation, excessive indebtedness, personal insecurity."

In a display of legislative muscle, ruling party deputies used their majority to elect an all-Chavista leadership, beginning with Mr Cabello, a former military officer who is regarded as the country's third most powerful man.

Watching the vote and debate from the balcony of the chamber was Maduro, Mr Chavez's handpicked successor who has sought to squelch reports of a power struggle with Cabello.

Outside the National Assembly, hundreds of Chavistas, dressed in the flaming red of his socialist revolution, chanted for their cancer-stricken leader with almost religious fervor.

"I love him, I want him and I hope he recovers," said Ms Maria Mateus, chanting with friends outside the palatial Spanish colonial-style building: "Here the one who rules is Chavez, and the revolution." "And he will return! He will return! The comandante will return!" shouted another group of supporters.

Mr Chavez, 58, is recovering in Havana from his fourth and most difficult round of cancer surgery, his condition clouded by serious complications that have raised doubts about his fitness to serve.

So far, he has refused to relinquish the office, leaving Maduro in charge of running the country without transferring the full powers of the presidency.

In a speech to supporters outside the National Assembly, Mr Maduro said he would remain as vice-president until there is a swearing-in.

"I continue in office and some day when there's an opportunity to swear me in - it's a formality - it will be done," he said.

On Friday, arguing for continuity, Maduro laid out a legal rationale for indefinitely delaying Mr Chavez's swearing-in without his giving up the powers of the presidency, even on a temporary basis.

The country's main opposition coalition insists that Mr Chavez must take at least a temporary leave if his health keeps him from taking the oath of office on Jan 10, a date established by Venezuela's constitution.

Under the constitution, new elections must be held within 30 days if the president dies or is permanently incapacitated either before he takes office or in the first four years of his six-year term.

But Mr Maduro rejected opposition calls for Mr Chavez to be declared temporarily incapacitated if he fails to show up for the swearing-in on the date set by the constitution.

With a pocket-sized constitution in hand, Mr Maduro argued that the charter provides "a dynamic flexibility" that allows the president to take the oath of office before the Supreme Court at some later date.

Analyst Luis Vicente Leon said nothing can stop Mr Chavez from staying in the presidency after Jan 10.

"There are no independent institutions nor solid political organisations that can prevent a suspended swearing-in," he said in a tweet Saturday.

The government said this week that since undergoing surgery last month in Havana, the president has developed a "serious pulmonary infection" that has led to a "respiratory insufficiency."

Mr Chavez was re-elected on Oct 7 despite his debilitating battle with cancer and the strongest opposition challenge yet to his 14-year rule in Venezuela, an Opec member with the world's largest proven oil reserves.

Cancer was first detected by Cuban doctors in June 2011, but the Venezuelan government has never revealed what form of the disease Mr Chavez is battling.