Venezuela will postpone Thursday's presidential inauguration due to President Hugo Chavez's continuing health problems, the government said.

The 58-year-old has not been heard from or seen in public since his 11 December cancer surgery in Cuba.

The constitution says the president should begin a new term on 10 January.

"(Chavez's) medical team has recommended that the postoperative recovery should extend past Jan 10," Vice President Nicolas Maduro said in a letter read out to the National Assembly.

The letter did not say when the inauguration would take place or provide any time frame for Mr Chavez's recovery.

The delay is another sign that Chavez's battle with an undisclosed form of cancer in the pelvic region may keep him from ruling for a third term.

His resignation or death would upend politics in the oil-rich country that has grown accustomed to his charismatic but controversial leadership.

The constitution does not specify what happens if the president does not take office on 10 January.

Government leaders insist Mr Chavez is completely fulfilling his duties as head of state, even though official medical bulletins say he has a severe pulmonary infection and has had trouble breathing.

Opposition leaders insist the government is running roughshod over the constitution by ignoring the specified inauguration date.

They insist Congress head Diosdado Cabello, a key Chavez ally, should step in as a temporary president while Chavez recovers.