Protesters are holding several policeman hostage after clashes in Peru claimed at least 33 lives.
Indigenous demonstrators are also threatening to set fire to an oil pumping station.
They are demanding the government tell police to halt efforts to clear weeks of blockades of roads and rivers that have hurt food and fuel supplies.
Up to 38 police officers could be held hostage.
Those killed included at least 22 tribesmen and nine policemen. The violence took place as security forces tried to end a road blockade.
There have been fuel and transport blockades in Peru's Amazon region for almost two months.
Local people say new laws will make it easier for foreign companies to exploit their land for natural resources.
The fighting took place at a jungle highway near the town of Bagua, more than 1000km north of the capital, Lima.
They are the most serious to have broken out since indigenous groups began a protest campaign in April.
They are opposed to plans by the government of President Alan Garcia to open up communal jungle lands for oil exploration, logging, mining and large-scale farming.
Indigenous leaders say police using helicopters opened fire on demonstrators in the latest incident.
One indigenous leader, Alberto Pizango, told reporters he held the government responsible for the killings, which he said had taken place during a peaceful demonstration.
The authorities say the police were fired on first, and Mr Garcia accused the Indians of "falling to a criminal level."
Earlier this month, Peru's military was authorised to give support to police in the escalating dispute.
Mr Garcia has said all Peruvians should benefit from the country's natural resources not just the people who happened to live in the areas concerned.
Under Peru's constitution the state owns the country's mineral and hydrocarbon wealth.
