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Silvia Izquierdo, Associated Press
Workers repave the plaza in front of the "Arcos da Lapa," an aqueduct converted into a trolley bridge in Rio de Janeiro, Brazil, Wednesday Feb. 1, 2012. In the past year, a trolley car ran off the arches' rails, killing five and injuring dozens and a French tourist fell to his death while riding the same car because of a hole in a security fence along the track's edge. These accidents are contributing to a growing concern about Rio de Janeiro's readiness to host the finals of the 2014 World Cup as well as the 2016 Olympics.

RIO DE JANEIRO — Enormous buildings suddenly collapse in this seaside Olympic city's center, killing 17. A manhole explodes near Copacabana Beach, severely burning a pair of American tourists.

Another explosion rips through a downtown restaurant, blasting the bodies of three workers clear across the street. A trolley car that's a favorite attraction for visitors runs off its rails, killing five and injuring dozens. A French tourist falls to his death while riding the same line because of a hole in a security fence along the track's edge.

These accidents from the past year haven't just highlighted everyday dangers for Rio's 6 million residents. They are contributing to a growing concern about Rio de Janeiro's readiness to host the finals of the 2014 World Cup as well as the 2016 Olympics.

Rio's Mayor Eduardo Paes argues that last week's unexplained building collapse and other infrastructure woes are not directly related to preparations for the World Cup or the Olympics because none of the accidents occurred at the sites planned for either event.

But critics say the repeated deadly accidents in the heart of the city point to larger problems: decades of neglect and almost nonexistent urban planning, lax oversight and institutionalized corruption, that could spell disaster at the World Cup or Olympics.

With its sprawling sandy beaches, palm tree-lined streets and rocky outcroppings covered with lush, tropical vegetation, Rio is a picture postcard of a city. But scratch the surface and it soon becomes apparent that the decay here runs deep, and extends far beyond the infamous hillside slums, or "favelas."

Aging natural gas pipelines crisscross the subterranean network of electricity lines, a dangerously combustible mix thought to explain a rash of exploding manholes in the past year, with the latest blowout coming this week.

Even moderate rains, and Rio is a city of immense downpours, suffice to turn many thoroughfares into rushing rivers, including the area around iconic Maracana stadium, the jewel in the 2014 World Cup crown and venue for the opening of the Olympics.

If that weren't enough, Rio is also dotted with more than 1,500 abandoned buildings, many of them in advanced states of disrepair, according to a recent report in Veja newsweekly, citing city authorities.

Last Wednesday's dramatic disintegration of a 20-story office building added to the doubts about Rio's capacity to play host to world-class events, with photos of the wreckage splashed across newspapers and websites the world over. Seventeen bodies have been retrieved and three people are still missing, but casualties could have numbered in the hundreds had the building fallen during the workday instead of at night.

Authorities are still investigating the cause of the collapse, which also pulled down two neighboring buildings, but officials have pointed to illegal construction inside the structure as the likely culprit.

"You can't imagine this happening in the financial center of New York or Paris or even Beijing," said Christopher Gaffney, an American academic who's a visiting professor at the graduate school of architecture and urban planning at the Fluminense Federal University in Rio's sister city, Niteroi. His research focuses on preparations for the World Cup and Olympics.

"In Rio, structural engineering is not the problem," Gaffney said. "The problem is management of the city ... It's a totally unregulated system, which leads to problems" such as the exploding manholes, derailing streetcars and collapsing buildings.

Rio authorities' laissez-faire attitude dates back hundreds of years to colonial days and is in part a legacy of the Portuguese settlers' penchant for bureaucracy, Gaffney said. The civil codes here are so thick with regulations that it would be almost impossible for construction companies to follow them to the letter, so in practice virtually no one pays them heed at all.

In the days since the collapse of the buildings, Rio authorities have registered more than 100 tips from locals blowing the whistle on illegal construction, according to local media reports.

"There's no municipal oversight — even though there is, it's on the books — but in practice it's not done. That's how the city has been built for centuries," said Gaffney. "But with the World Cup and the Olympics on the horizon, how do you change that to put on a good face? How do you bring millions more people into a system that's fantastically fragile?"

World Cup organizer FIFA appears to be asking itself the same question.

World football's governing body has repeatedly blasted Brazil for lagging in preparing for the 2014 tournament, not to mention the 2013 eight-team Confederations Cup, the warm-up event that is also meant as a test run for the World Cup host nations. Not one of the 12 slated stadiums being built or renovated is finished, and worker strikes over pay and conditions have exacerbated the delays.

The Cup's dozen host cities are thousands of miles apart, dotted over the far corners of this giant nation, and Brazil's ailing airport infrastructure has yet to receive the upgrade FIFA says it needs.

The organization's exasperation with Brazil is such that local media reports here were abuzz with rumors that the organization's secretary general, Jerome Valcke, had threatened to strip Brazil of the 2014 tournament. Such a move would be permitted under FIFA regulations, although it's seen as extremely unlikely.

There are hopes that last week's building collapses will help bring more transparency in the bureaucracy and encourage more effective government oversight.

"Wednesday night it once again became clear that authorities know how to handle emergencies," read an editorial in Rio's O Globo newspaper a day after the disaster. "What's missing is preventive action, not only to protect the public but also to educate them on how to follow the rules."

Still, Brazilian media was quick to dismiss any suggestion that Rio's recent rash of tragedies bodes poorly for the upcoming events.

"One thing has nothing to do with the other," read an editorial in the Jornal do Brasil online daily. "Unfortunately, accidents like these can happen in any country.

It added: "Despite all the attacks and all the rooting against Rio, the city will enchant the world, as it always does."