A UN representative and three other people have been taken hostage by Indians, and federal officials were flying to the jungle on Monday to negotiate their release.
The Cinta Larga Indians invited David Martins Castro, a representative of the UN High Commission for Human Rights, to a meeting on Sunday on their reservation. Martins came with a federal prosecutor and two other people, but the Indians prevented all four from leaving.
"Right now the situation is calm, the hostages are being well treated. We are only waiting" for Federal Indian Bureau President Marcio Meira to negotiate, police inspector Rodrigo Carvalho said by phone from the state capital of Rondonia.
Meira was flying to the reservation on Monday to negotiate their release, said a spokeswoman who declined to be identified according to agency policy.
Diamond mining is at the heart of the conflict: The Indians are demanding that federal police -- now posted at the reservation to prevent illegal diamond trafficking -- allow Indians to come and go more easily. They also want better health care, education and job opportunities.
Hostage takings are a fairly common tactic among Amazon Indians and the situations are usually resolved within hours or days.
But the Cinta Larga have a fierce reputation. In 2004, they massacred 29 illegal wildcat diamond miners on their remote reservation, which holds what is believed to be the largest diamond lode in South America.
The massacre ended a four-year-long diamond rush by miners from across Brazil who had converged on the 2.7 million hectare reservation. Twenty-eight Indians have been charged in the massacre, but the case has stalled over jurisdictional questions about the special status of Indians and their reservations under Brazil's Constitution.
Brazilian law bans mining of any kind on Indian reservations, but in recent years, federal authorities have opened some exceptions for Cinta Larga to sell their diamonds.
Under pressure from the Cinta Larga, Brazilian legislators are considering changing the law to allow mining by Indians on reservations. But the move is opposed by some Indian rights group that fear the easy money will destroy the Indians' culture.
Mining companies also are lobbying to be allowed on to reservations, paying the tribes royalties.



