President Hugo Chavez has been receiving chemotherapy since recovering from a severe respiratory infection in mid-January and "continues his battle for life," his vice-president said late Friday.

Vice-President Nicolas Maduro suggested the chemotherapy was continuing in the government's first mention of it as among treatments that Venezuela's cancer-stricken president has received since his Dec. 11 cancer surgery in Cuba.

Hugo Chavez, posing with his daughters, had been undergoing treatments in Cuba. (Presidential Press Office/AP)

Maduro made the disclosure after a Mass for Chavez in a new chapel outside the military hospital where authorities say the socialist leader has been since being flown back to Caracas on Feb. 18.

The vice-president quoted Chavez as saying he decided to return to Venezuela because he was entering "a new phase" of "more intense and tough" treatments and wanted to be in Caracas for them.

Maduro's offering of the most detailed rundown to date of Chavez's post-operative struggle came hours after an accusation by opposition leader Henrique Capriles that the government has repeatedly lied about Chavez's condition.

"We'll see how they explain to the country in the [coming] days all the lies they've been telling about the president's situation," Capriles, whom Chavez defeated in Oct. 7 elections, said in a tweet.

Chavez has not been seen nor heard from since going to Cuba for his fourth cancer surgery, except for a set of "proof of life" photos released Feb. 15 while he was still in Havana.

Chavez first revealed an unspecified cancer in the pelvic region in June 2011, and reported undergoing radiation treatment and chemotherapy after earlier operations.

The government has sent mixed signals on Chavez's condition, although Maduro has said several times that Chavez was battling for his life. He repeated that Friday, and also accused opponents of spreading rumours about Chavez's health to destabilize the nation.

Respiratory infection

Maduro, Chavez's chosen successor, said his boss' condition was extremely delicate over New Year's as he battled a respiratory infection that required a tracheal tube.

"In mid-January he was improving, the infection could be controlled, but he continued with problems of respiratory insufficiency. Afterward, there was a general improvement, and the doctors along with President Chavez decided to initiate complementary treatments," Maduro said.

Venezuela's Vice President Nicolas Maduro says Chavez is continuing with chemotherapy. (Fernando Llano/Associated Press)

"You know what the complementary treatments are, right? They are chemotherapy that is applied to patients after operations."

Cancer specialists couldn't be reached immediately for comment on Maduro's announcement. But oncologists have said that chemotherapy is sometimes given to slow a cancer's progression, ease symptoms and extend a patient's life.

The opposition says Chavez should either be sworn in for the new term he won in the election or declare himself incapable and call a new election. The constitution says he should have been sworn in on Jan. 10, but Venezuela's Supreme Court said it was OK to wait.

Earlier Friday, Maduro accused the Spanish newspaper ABC and Colombia's Caracol network of spreading lies about Chavez's condition.

ABC said without specifying its source that Chavez's cancer had spread to a lung. It said he had been moved to an island compound in the Caribbean.

Chavez's son-in-law, Science Minister Jorge Arreaza, said on state TV that Chavez continues "to fight hard and is in the military hospital, as peaceful as he could be, with his doctors, with his family."