Hundreds of indigenous people protesting the construction of a road in Bolivia's Amazon basin region marched Sunday toward the capital, La Paz, their leaders said.

"We walked starting at 3:00 am" for 31 kilometers (19 miles), said march leader Adolfo Chavez.

He did not say precisely when demonstrators would be in La Paz. But what lies ahead, only in terms of the march: crossing the Andes at a staggering 4,600 meters (15,000 feet).

Indigenous people angry at the plans to build a highway through an Amazon nature reserve had been holding off and on protests for months -- even after President Evo Morales technically suspended the project and publicly apologized for earlier violence.

Following widespread uproar, Morales, who backs the road, called for an international investigation into the police crackdown and arrests of hundreds of activists who had been marching for a month.

Rights observers from the Office of the United Nations High Commissioner for Human Rights (OHCHR), the Organization of American States (OAS) and the Union of South American Nations (UNASUR) said last week they would form a commission to carry out a probe of abuses earlier during the march.

But there has been no sign of the government winning local peoples' trust, which will be tough after it offered dialogue but then cracked down on marchers.

And the Brazil-financed road is threatening to run through the Isiboro Secure reserve, home to some 50,000 natives from three different indigenous groups. These isolated groups, from the humid lowlands, are not the main indigenous groups that make up most of Bolivia's population, the highland Andean Aymara and Quechua peoples.

The lowland people fear their traditional lands may be overrun by landless highland farmers.

Police fired teargas and 74 people were injured in the September 25 crackdown, according to official figures.

Morales -- who is Bolivia's first democratically elected indigenous leader himself -- came to power on a wave of indigenous support; former interior minister Sacha Llorenti, who later resigned, denied ordering the crackdown. The defense minister and migration chief also resigned.

The dispute is a major challenge for Morales, who has said the 300-kilometer (185-mile) highway is vital for the country's economic development.

The road is part of a network linking landlocked Bolivia to the Pacific Ocean through Chile and the Atlantic Ocean through Brazil.