Armed with shotguns and bows and arrows, thousands of Brazilian Indians invaded ranches near the border with Paraguay to claim what they say is ancestral land, state officials and police said on Sunday.
Wearing war paint and masks, Guarani and Caiua Indian families began to occupy ranches near the towns of Japora and Iguatemi in Mato Grosso do Sul state before Christmas.
Local ranchers claim they have killed livestock, held hostages and expelled people from their property, police said.
"They are walking all over these ranches as if it were their own land," Military Police officer Jose Bezerra said.
The center-left government of President Luiz Inacio Lula da Silva has promised to increase the redistribution of land to Indians who have suffered discrimination for centuries.
Brazil's Indian agency says they will hold an area equivalent to half the size of Europe, or 12 percent of the nation, after extra demarcations of ancestral land take place.
In the current conflict in the border area 390 km (240 miles) south of Mato Grosso do Sul state capital Campo Grande, Indians claim ranchers are on public land that is ancestral Indian territory or land demarcated them by the government.
"The municipalities haven't handed over land promised to them," said Adao Irapiuta Brasil, who represents the Guarani and Caiua at Brazil's Indian agency, the National Indian Foundation. "They often only hand it over when force is used."
Irapiuta said at least 20,000 of the 48,000 Guarani and Caiua living in the region had taken part in occupations on 16 ranches since the invasions began.
Federal and military police put the numbers much lower but said at least a thousand Indians had invaded up to five ranches near Japora in recent days.
Police are investigating claims Indians killed 10 cattle at the Agrolack ranch near the village of Porto Lindo. The ranch's manager was not immediately available for comment.
Police are also looking into claims that Indians held captive and expelled people on other ranches near Japaro and Sao Sebastiao.