Venezuela's government has revealed for the first time that President Hugo Chavez has been receiving chemotherapy as he "continues his battle for life".

After a Mass for Mr Chavez vice president Nicolas Maduro said doctors began chemotherapy treatment for the cancer-stricken socialist leader after he recovered from a respiratory infection in mid-January.

Mr Maduro did not specify what treatments Mr Chavez was currently receiving.

The government says Mr Chavez was flown back to Caracas on February 18 and has been at the city's military hospital since.

He has not been seen nor heard from since his December 11 surgery in Cuba for an unspecified cancer in the pelvic region.

He first revealed his cancer in June 2011 and previously reported undergoing radiation treatment and chemotherapy.

Opposition leader Henrique Capriles accused the government of repeatedly lying about Mr Chavez's condition and said the truth would be known within days.

Mr Capriles tweeted the claim yesterday as Mr Maduro assured Venezuelans on national TV that their president continued a difficult and slow recovery..

"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," said Mr Capriles, whom Chavez defeated in an October election.

Chavez's son-in-law, science minister Jorge Arreaza, one of a small circle with access to the president, said on state TV that Mr Chavez continued "to fight hard and is in the military hospital, as peaceful as he could be, with his doctors, with his family".