Rio's state government will build seven miles of concrete walls around some of the biggest slums in an effort to halt deforestation of the jungle surrounding the metropolis, officials said Tuesday.

Walls reaching 10-foot-high will be built this year around sections of at least 11 slums, said Icaro Moreno, president of the state's public works department. The project will cost $17 million.

Standing atop the Dona Marta slum in the shadow of Rio's famed Christ statue, Moreno pointed to a 100-yard section of the first wall under construction. Work began a few weeks ago.

"Each year that passes we're losing more of the Atlantic rain forest," Moreno said, gesturing toward to the lush green jungle on the other side of the wall. "Now, we're setting limits on where these communities can expand."

Brazil's National Institute for Space Research, which monitors forest destruction, reported in December that between 2005 and 2008, deforestation of Rio's urban rainforest had doubled as compared to the previous three years.

About 506 acres were destroyed in the last three years — most of which officials blame on the expansion of slums as more newcomers from Brazil's interior arrive in this city of 6 million people.

Some 600 houses in the 11 slums will have to be destroyed to make way for the walls, Moreno said. People living in those homes will be provided with new housing the state is constructing inside the slums.

Some rights groups have suggested the walls are being constructed to segregate the slums from the richer areas of Rio, a city where those mired in poverty can gaze into the windows of luxury high rises, Many of the slums — called "favelas" — are built on the steep mountains that dot Rio's landscape and look down on the wealthy, beach front areas.

Moreno rejected the criticism, saying the only objective is to protect the rainforest. The government is planning to build walls around at least 40 slums by the end of next year, he said.

In Dona Marta, residents mostly shrugged off the controversy surrounding the construction of the wall.

Poking her head out the window of her small wooden shack sitting just meters away from the wall, Maria da Graca Martins da Silva, who has spent most of her 62 years living in the slum, chuckled when asked if the wall would be a good or bad thing for the community.

As workers in blue uniforms and hard hats lugged 110-pound sacks of cement up painfully steep stairs in front of her abode, Silva said most people living in Dona Marta didn't see the wall as segregating them from the rest of Rio, anymore than the poverty they lived in — though doubts lingered.

"We don't feel imprisoned. But, I wonder about one thing: Is this wall going to curtail our freedom? I hope not," she said.

Silva's home is one slated to be destroyed to make way for the wall. She said she was happy the government was going to give her a new home — but also expressed a some skepticism.

"I think it is a good project," she said. "But only if they really build new homes for us."