Amazonian campaigners have pledged not to back down
Human rights lawyers have accused Peru's government of a cover-up, after clashes between police and indigenous protesters killed at least 50 people.
The lawyers say hundreds more may be missing, amid rumours that the police have hidden bodies. But they say rights groups cannot get in to investigate.
The government denies the claims and says police were the victims.
For two months Amazonians have rallied against laws which they say will open their lands to oil and gas drilling.
The government of President Alan Garcia - a hate figure for the protesters - insists it has guaranteed millions of acres for native people.
Meanwhile, Nicaragua has granted political asylum to indigenous leader Alberto Pizango.
He sought refuge in the country's embassy in Lima after an arrest warrant was issued on charges of sedition, conspiracy and rebellion.
'Truth will come out'
The violence erupted last Friday when more than 2,000 Indians - many of them carrying spears and machetes - launched a protest over the drilling plans.
About 30 protesters and 24 police officers were killed in the worst clashes for at least a decade.
After visiting the area, near the town of Bagua Grande, 1,400km (870 miles) north of the capital Lima, rights lawyers said hundreds of people could not be accounted for.
One of the lawyers, Ernesto de la Jara from the Institute for Legal Defence, urged the government to begin an independent judicial investigation.
"I say to the authorities they should take care because sooner or later the facts of what happened will come to light," he said.
"Dead bodies may be covered up for now but, little by little, the truth will come out and they will have to respond."
The BBC's Dan Collyns, in the town of Bagua Chica, says indigenous groups are insisting that the government be tried for crimes against humanity.
But the government denies any wrongdoing and has launched a publicity campaign portraying the murders of policemen as acts of savagery.
"It has been irrefutably proven that the police were tortured and killed," Maria Zavala, Peru's ambassador to the Organization of American States, said in a speech in Washington.