Bolivian police used tear gas and truncheons to break up a march Sunday by hundreds of indigenous activists protesting plans to build a highway they say will despoil a vast Amazon nature preserve.
Police arrested the march's leaders, hauling them away in buses. Bolivia's national ombudsman, Rolando Villena told Erbol radio "there was excess use of force" by police in "violating the rights of the Indians in the protest."
The U.N.'s representative in Bolivia, Yoriko Yasukawa, called on the government to rely on dialogue.
Witnesses including an Associated Press photographer saw about 500 police surround protesters, including woman and children, just before dusk Sunday and set upon them with gas and clubs.
The government had no immediate statement on the crackdown but police officers on the scene told the AP that there were injuries on both sides, including police struck by rocks.
About 1,000 marchers opposed to the highway had departed the eastern lowlands provincial capital of Trinidad in mid-August and were nearing La Paz, the capital.
The police action came a day after protesters armed with bows and arrows briefly detained Foreign Minister David Choquehuanca, forcing him to march with them to protect them from police and from pro-government demonstrators.
Interior Minister Sacha Llorenti accused the protesters of "kidnapping" Choquehuanca.
President Evo Morales, this poor landlocked nation's first indigenous president, has insisted the highway is necessary for development but on Sunday said he would submit the highway's fate to a regional referendum.
Morales' stubborn backing of the highway has alienated many of the core supporters who ensured his December 2009 landslide re-election by insisting on the 190-mile (300-kilometer) Brazil-financed highway.
Environmentalists say the highway, which will connect Brazil with Pacific ports in Chile and Peru, will mostly benefit Brazilian commercial interests such as logging exporters while endangering a pristine, 600-square-mile (12,000-square-kilometer) nature preserve.
The Isiboro-Secure Indigenous Territory National Park is home to 15,000 natives, who live off hunting, fishing, gathering native fruits, and subsistence farming.
The natives fear an influx of settlers will destroy rich natural habitats,felling trees and polluting rivers.
The road is to be built with a $415 million loan from Brazil's national development bank, and a Brazilian company, OAS, has the green light to begin toppling trees.
Edwin Alvarado, spokesman for Bolivia's Environmental Defense League, or LIDEMA, has called the highway a pretext for eventual oil exploration in the rain forest.
Under a 2009 constitution championed by Morales, the country's indigenous groups must be consulted in advance about any projects that might affect their traditional lands.
The law does not give them veto power, however.
Associated Press writer Frank Bajak contributed to this report from Lima, Peru.