Government leaders are defending the reliability of Brazil's power grid after a huge blackout left nearly 60 million people in the dark and raised concerns about its ability to guarantee electricity for a surging economy.

Energy Minister Edison Lobao said the hours-long blackout Tuesday night was caused by heavy rain, lightning and strong winds that made transformers on a vital high-voltage transmission line short circuit, leading two other lines to go down as part of an automatic safety mechanism.

The massive Itaipu dam on the border with Paraguay — the world's second-largest hydroelectric power producer — was completely shut down for the first time in its 25-year history during the blackout, but Loboa stressed the plant was not the problem.

"The problem was exclusively with the transmission lines," he said Wednesday.

The blackout cut electricity to 18 of Brazil's 26 states and left them without power for up to four hours. About 7 million people also lost water service in Sao Paulo. All of Paraguay briefly lost power.

Analysts said the blackout shows Brazil's lack of investment in the power system at a time when Latin America's largest economy is booming and the country is preparing to host the 2014 World Cup and 2016 Olympics.

The Brazilian Olympic Committee would not comment on the power failure. But among guarantees made to the International Olympic Committee is that Rio, as the host city in 2016, will be isolated from the nation's power system — to avoid problems like this. The city will have its own direct energy feed during the Games.

"There is an absolute failure of infrastructure in terms of energy," said Patrizia Tomasi, an engineer with the Brazilian energy consulting firm Planck E. "What we are seeing now is only the beginning. There is a need to invest more, to improve how energy is managed by those in the government. We have Itaipu, which is huge, which is great, but there are no lines to transmit all that energy."

President Luiz Inacio Lula da Silva disputed that the government has not done enough to improve the power grid since he took office in 2003, two years after Brazil suffered shortages and rationing under his predecessor.

"In seven years, we created 30 percent of all the transmission lines built in the last 130 years," Silva said. "There was no shortage of power generation, and the problem was not a lack of transmission lines."

Lobao said Silva's government has invested about $13 billion in transmission lines and $4.7 billion more on transformers since 2003.

The energy minister also defended the strength of the Brazilian system — pointing out it took a day to fully restore power after a blackout hit the East Coast of the U.S. and Canada in 2003, leaving 50 million people in the dark. He mentioned lengthier blackouts in other nations, including Italy and Japan.

It was at least the fourth time since 1985 that Brazil has suffered a mammoth power outage blamed on transmission line failures from Itaipu.

The worst of the blackouts occurred in 1999 after lightning struck a power substation in Sao Paulo state, plunging 97 million Brazilians into darkness for up to five hours.

After severe energy shortages and rationing in 2001, Brazil diversified its energy supply. It has seen blackouts since, but none like Tuesday's failure, in which the power outage was more geographically widespread. Analysts say the scope of the blackout was so large because the nation's power grid has become more interconnected, meaning a glitch in one part can affect a wider area.