President Chavez's party faces a tough electoral battle next month

A massive power cut has left millions of Venezuelans without electricity on Sunday, the third big outage this year.

The blackout hit several of the country's most populous states, including the capital, Caracas.

Venezuelan President Hugo Chavez praised officials for quickly detecting and beginning to repair the fault.

Mr Chavez says upgrading the grid after years of under-investment will take time but rejects criticism that nationalisation has made things worse.

The blackout happened mid-morning on Sunday, affecting about a third of the country.

In the capital, power was down for at least an hour, while in some other regions it was double that.

"Technically there is no reason for the failure," the head of the state electricity corporation, Hipolito Izquierdo, told state television.

"It's strange and worrying that a blackout of this size should happen on a Sunday, when demand is much below the daily average and when there is no great demand from industry," he said.

The two previous power cuts were during the week.

Sunday's blackout happened when a major electricity distribution line, supplying about 70% of the electricity consumed in the country, failed, officials said.

President Chavez, speaking during a visit to a gas pipeline project, said officials had detected and begun repairing the fault in 15 minutes.

"That's what you call efficiency," Mr Chavez said.

November elections

The president, who has announced big investment in the national grid over the next five years, again urged Venezuelans to use electricity sensibly.

The sector has been completely in state hands since 2007 but Mr Chavez has said nationalisation has not contributed to the current problems.

He says the private companies who used to be in charge failed to make the necessary investment to upgrade the system to cope with increasing demand.

Venezuela holds state and municipal elections next month, amid indications that Mr Chavez's United Socialist Party of Venezuela (PSUV) could face tough fights in some areas.

Mr Chavez, who last December suffered his first electoral setback when his plans for constitutional change were defeated, has called the forthcoming vote the most important in the history of Venezuela.

Analysts say power cuts could come to symbolise what some voters feel are the president's failings in running the country.