Many of the protesters are indigenous Bolivians

Only a quarter of the legislators managed to reach the Congress building for its first session in over a week.

Thousands of people converged on the political capital, blocking traffic and bringing the city to a standstill.

President Carlos Mesa has accused protest leaders of organising a coup by trying to prevent access to Congress.

Lawmakers from the two houses of Congress had planned to debate a controversial bill that sets out how greater autonomy will be given to Bolivia's regions.

But many could not reach the Congress building, which was ringed by heavily armed riot police, soldiers and armoured vehicles.

Police fired tear gas and water cannon to try and break up the crowds who included miners, students and farmers, many of them indigenous Bolivians.

Resources battle

The protesters, mainly from the impoverished highlands, want to stop the Congress granting autonomy to the wealthier eastern and southern provinces.

They are also demanding the nationalisation of the Bolivian energy industry, saying a law which increases taxes on foreign gas investors, does not exert enough control over the country's resources.

Protesters say that the new law does not go far enough

President Mesa has said the gas law is too punishing for the multinationals that have invested billions of dollars in Bolivia's gas fields.

A similar dispute led to the overthrowing of Mr Mesa's predecessor, Gonzalo Sanchez de Lozada, in October 2003.

The president has vowed to remain in office for his full term, despite frequent political crises.

He is backed by the armed forces, which last week sacked two officers after they claimed to represent a new nationalist movement in the military.