Venezuelan President Hugo Chavez has said that he will have to have further surgery after doctors found a lesion during medical tests in Cuba.
The 57-year-old had two operations in Havana last year to remove a cancerous tumour from his pelvis, and had said he was completely recovered.
He said the lesion was in the same area but was small.
Mr Chavez – who has governed Venezuela for 13 years – is due to stand for re-election in October.
He revealed the news of his illness during a televised tour of a factory in his home state of Barinas.
“The truth is that in the examination in Havana they detected a lesion in the same place where the tumour was extracted almost a year ago,” he said.
“There is no metastasis. It is a small lesion of around 2cm, very clearly visible. This lesion must be removed,” he explained.
He said the surgery would take place “in the coming days”.
“I am in good physical condition to confront this new battle,” he added.
The announcement followed unconfirmed reports in the Venezuelan media that Mr Chavez had travelled to Cuba for urgent treatment.
On Monday his Information Minister, Andres Izarra, dismissed the reports as part of a “dirty war” against the government.
Mr Chavez also accused the opposition of spreading rumours and wishing him dead.
“They are trying to create anxiety and panic, and to destabilise the country,” he said.
The exact nature and extent of Mr Chavez’s condition has never been made public, fuelling persistent rumours that it may be worse that he has indicated.
Mr Chavez had surgery to remove the tumour – which he said was the size of a baseball – in Cuba last June.
He also had chemotherapy, and last October last year announced he was cancer-free.
His challenger in October’s presidential election is Miranda state governor Henrique Capriles Radonski, who won an opposition primary earlier this month to chose a unity candidate.
Mr Capriles has previously said he hopes Mr Chavez leads a long life, “so he can see the changes that are coming in Venezuela”.