President Carlos Mesa accused protest leaders of organising a coup.

"There is no democracy without parliament," he said, in a speech to the military. "The closure of congress is a coup d'etat."

The protests remained peaceful on Monday but there are concerns they may be stepped up on Tuesday, when Congress meets for the first time in weeks to discuss the political agenda.

'We won't leave'

The mainly indigenous protesters are demanding the nationalisation of the Bolivian energy industry, saying a law passed by congress, that increases taxes on foreign gas investors, does not exert enough control over the country's resources.

They are also demanding regional autonomy and changes to the constitution.

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.

But the protesters said they would stay in La Paz until they had achieved their aims.

"We want our gas to be processed here in our country, so that more money is available for teachers like us. We only earn 800 bolivianos ($100) a month," said Basilio Arcaya, who has travelled to the capital from the city of El Alto every day for the last two weeks.

"The government thinks we are going to get tired and leave, but it won't happen," he told Reuters.