Bolivian police in recent days have arrested 15 people allegedly linked to the ambush in La Paz in which three anti-drug agents and a doctor died, a government official told Efe on Wednesday.

Of the 15 people arrested, three have dual nationality - Bolivian and Peruvian - although the authorities say that this is a preliminary evaluation, the deputy minister for internal government, Jorge Perez, said.

"We don't want to move forward too quickly on the matter of foreigners. We have information that they participated in the attack, but we don't want to go too far on that. We want to be completely certain. So, this is being handled as preliminary information," Perez said.

A judge sent nine of the detainees to prison, one woman was released on parole and the legal situation of the rest still has not been defined, judicial sources say.

The members of the group are accused of carrying out an ambush supposedly staged by peasants and alleged foreigners linked to drug trafficking last Saturday in the town of Apolo, located 450 kilometers (279 miles) north of La Paz, near the border with Peru.

Authorities say that the group violently resisted the entry into the zone by soldiers and police belonging to the Joint Task Force charged with destroying illegal coca leaf plantations.

Coca leaf is the raw material from which cocaine is made.

Two soldiers, a police officer and a physician died in the attack, 12 people were wounded by gunfire and six people who were taken hostage were later rescued.

In Apolo there is a zone where the legal cultivation of coca is authorized, but there are also communities where coca plantations are allegedly devoted to growing the product to illegally make cocaine.

President Evo Morales called the attack on the police and soldiers "criminal" and blamed minority groups allegedly headed by Peruvian drug traffickers.

Peasants living in Apolo said that no ambush took place, but rather there was an armed clash with task force members, whom they accused of violently entered several homes, but Interior Minister Carlos Romero said Wednesday that the task force was attacked. EFE