SAO PAULO (Reuters) - Brazil's president denied on Wednesday that underinvestment was to blame for the worst power outage in a decade, which left a huge swath of the country in the dark for more than five hours and raised doubts about the reliability of its energy infrastructure.
The blackout on Tuesday night left tens of millions of people without power across most of the country's wealthy southeastern region, halting subways and snarling traffic in major cities like Sao Paulo and Rio de Janeiro.
President Luiz Inacio Lula da Silva summoned his energy minister, Edison Lobao, for an urgent meeting in Brasilia on Wednesday to explain what triggered the outage.
Energy officials said it was likely caused when a storm downed three transmission lines carrying power from the giant Itaipu hydroelectric dam on Brazil's border with Paraguay.
"We didn't have a failure in the generation of energy, we had a problem in the transmission line," Lula told reporters in Brasilia, the capital.
Responding to criticism that the government has neglected to maintain and upgrade Brazil's energy infrastructure, Lula said investment in transmission lines over the last seven years amounted to 30 percent of what had been spent over the preceding 120 years.
Brazil's economy has forged ahead in recent years under former union leader Lula and was quick to shrug off the global financial crisis. But transport and energy infrastructure remain weak points for Latin America's largest country, which will host the 2014 World Cup and the Olympics two years later.
"The very long transmission lines in Brazil are very badly maintained," said Adriano Pires, director of the Brazilian Center for Infrastructure Studies in Rio de Janeiro.
"This shows that Brazil is very vulnerable. You can't leave a country the size of Brazil hostage to accidents."
An energy ministry official told Reuters the outage was triggered because the system was not equipped to cope with so many downed lines at once.
"The system is designed to withstand two contingencies ... here we had three," said Marcio Zimmermann, the ministry's executive secretary.
Zimmermann denied that the problem could have been caused by computer hackers. U.S. television network CBS reported in its "60 Minutes" program this month that blackouts in Brazil in 2005 and 2007 may have been caused by "cyber attacks," quoting mostly unnamed U.S. intelligence sources.
The blackout hit 18 of Brazil's 26 states. Paraguay, which gets about 90 percent of its power from the Itaipu dam, was left entirely in the dark for about 15 minutes. Paraguay's state electricity company said the problem originated in Brazil.
The last time Brazil suffered an outage on such a large scale was 1999, when a lightening bolt struck a transmission line in Sao Paulo state.
While some analysts said Tuesday's blackout highlighted the challenges Brazil faces to ensure its infrastructure keeps pace with its robust economic growth, others described it as an isolated incident that could happen anywhere.
"The system is reliable, even if it faces the risk of this sort of problem," said Cesar de Barros Pinto of Brazil's electrical transmission industry association.
Power was restored in Sao Paulo, Brazil's financial capital and South America's largest city, before dawn on Wednesday.
Traffic on the city's streets descended into chaos shortly after the power outage. Thousands of passengers were forced to exit stalled subway trains and walk along the tracks to get back to stations and make their way to the surface.
The city's streets were still clogged early on Wednesday after the mayor canceled restrictions on the amount of cars allowed to circulate during rush-hour traffic.
In Rio, the beachside city that will host the 2016 Olympics, many tourists left their hotel rooms along Copacabana beach because of the lack of air-conditioning and milled around on the darkened streets.
Additional reporting by Denise Luna and Rodrigo Viga Gaier in Rio de Janeiro, Brian Ellsworth in Sao Paulo and Daniela Desantis in Asuncion, writing by Stuart Grudgings, editing by Todd Benson and Cynthia Osterman