Nearby residents are furious. Desperate to prevent yet another slum from springing up next door, many grabbed weapons and ran into IndoAmerican Park, torching tents and chanting racist slogans. The squatters fought back, and at least three have died in waves of violence since the first land seizure last week, authorities said.

"It's an ugly situation," said Estela Gomez, 42, an Argentine who shares two "borrowed" rooms with 18 children and grandchildren in Ciudad Oculta.

Her family has marked off a shady spot under trees that are nearly as tall as the four-story slum buildings that crowd up against highway guardrails in the city, a legacy of past land grabs that officials failed to stop, and a grim reminder of the poverty that afflicts so many here and elsewhere in Latin America.

"We're demanding a roof with dignity," Gomez said. "Until they organize the slums, this is going to keep happening — people are going to keep seizing other areas."

They did Monday. Squatters invaded two more green areas, a private club's football field and property alongside a closed slaughterhouse.

Other activists blocked two freeways, one group demanding housing subsidies and another protesting the land grabs. As night fell, squatters and neighbors were lobbing rocks at each other over the football field's fence, with police nowhere around.

The land grabs — initially encouraged by activists who operate on the fringes of the ruling party — pose a political test for President Cristina Fernandez, a self-described leftist militant who has governed mostly by decree and who gives rousing speeches about the need to redistribute Argentina's wealth.

She blames the troubles on the refusal of Buenos Aires' center-right mayor, Mauricio Macri, to negotiate with squatters. But she also is struggling to restrain her more militant supporters, whose expectations are being raised with every promise made ahead of her expected run for re-election next year.

The anger swirling around the land grabs also reflects the anxiety many Argentines feel over social changes. This nation largely built by immigrants from Europe is struggling to accommodate an increasing flow of darker-skinned arrivals from poorer neighbors who compete for jobs and housing. Crime — often blamed on slum dwellers — is a concern.

Argentina's growing economy and open-door migration policies, which Fernandez celebrates as a humanitarian contrast to the U.S. crackdown on illegal immigration, have drawn more than 325,000 Paraguayans, 233,000 Bolivians and 50,000 Peruvians in recent years, the Geneva-based International Organization for Migration estimates.

Many of the newcomers have nowhere to settle but in slums known as "misery villages." All three of those reported killed in the violence at IndoAmerican Park were foreigners — a Paraguayan and two Bolivians.

More than 500,000 of the 10 million residents of metropolitan Buenos Aires lack decent housing, the capital's legislature determined this month. It's a phenomenon repeated in capitals across Latin America, where economies generally fail to provide for people in the provinces.

The latest land takeovers in Buenos Aires came just weeks after Brazilian police moved decisively into some of Rio de Janeiro's crowded shantytowns trying to root out drug traffickers as part of a pacification campaign.

"We need to show courage, like Lula did when he took charge of the fight against crime and drug trafficking," Buenos Aires' mayor said, referring to Brazilian President Luiz Inacio Lula da Silva.

Macri squarely blames Fernandez's populist approach for encouraging the slum dwellers.

"This is a result of uncontrolled immigration, that combines the arrival of honest people who come in search of work with criminal organizations, drug traffickers and mafias," Macri said. "This is how they begin to take control of areas of the city of Buenos Aires, especially the neighborhoods and slums that encircle the park."

Fernandez countered by accusing the mayor of incompetence and racism, and of encouraging the vigilantes.

"Here in Argentina, as in other parts of the world, immigrants do the work that in many cases our own citizens, because they have had a higher quality of life and better opportunities, don't do," she said. "This obligates us to be prudent, to be reflexive, not to stigmatize. There are bad people who commit crimes in all nationalities, in all colors and in all religions."

During Argentina's dictatorship, police moved in and bulldozed slums ahead of the 1978 World Cup. That legacy of brutality remains a constant thread in today's political discourse, and no one wants to be seen as responsible for blood in the streets. Macri's new capital police force — formed amid criticism that national police were failing to control crime — gave up trying to evict the first squatters last week after officers were televised beating several people.

Pablo Bellotti, a 39-year-old Argentine who has sold candy and flashlights at the city's subway stops for 20 years, now wields a cement-filled metal pipe to defend his stake in the park each night. It is his second attempt to get a subsidy by grabbing public land, he said.

"We did it once before, and the government said it would give us a little bit of money to pay the rent, but they didn't keep their promise. They didn't give us anything," he said. "Now there's nothing left for us but to join up with these Bolivians in search of a decent place to live."

While Bellotti and other Argentine squatters said they prefer getting a subsidy to building in the park, some Bolivian squatters are already planning to pour cement.

William Quispe and Nataly Montanio, a young couple from Cochabamba, Bolivia, huddled with their breast-feeding infant, Emanuel Matias, born six months ago in Argentina, in a teepee made with three tree branches and a blanket in a prime spot along the park's access road. Using tape and barbed wire, they marked off a plot 7 meters (23 feet) wide by 21 meters (69 feet) deep — enough for a multistory home with a little backyard.

"Our rent was expensive — 400 pesos, and my salary is 380," said Quispe, who stitches leather shoes together in a small factory — a job better than any he could find back home.

"The idea is to build here," he said. "We've already talked with our family in Bolivia to help us if we can build here. We all want a roof, so that we can stop renting."