An American missionary was shot to death in the Amazon state of Para on Saturday, less then a week after she accused loggers and ranchers of threatening to kill rural workers, authorities said.
Dorothy Stang, 74, was accompanying a group of peasants to a meeting with other local workers when they were attacked near the jungle town of Anapu, about 2,100 kilometres north of Sao Paulo. She was shot three times in the face, said federal police officer Fernando Raiol.
Two suspects had already been taken into custody, police said. It was not immediately clear how many people were involved in the attack. None of the other people in her group were reported injured.
Stang, of Dayton, Ohio, had lived in Brazil since the early 1960s and worked in the Amazon region for more than 20 years. She was an outspoken critic of efforts by loggers and large landowners to expropriate lands and clear large areas of the Amazon rainforest.
The Brazilian government compared the murder with the 1988 killing of Chico Mendes, the renowned rubber tapper who galvanised international attention to Amazon rainforest destruction.
"It's the type of crime that shows a profound disrespect to a democratic society, similar to the one that victimised Chico Mendes," Justice Minister Marcio Thomaz Bastos told the Estado news agency.
Last year, Stang, who was a naturalised Brazilian, was accused by the loggers of inciting violence in the region and supplying weapons and ammunition to the local people, a claim strongly denied by her family.
"She would not have gotten anything together as far as violence. Anything about her obtaining guns is absolutely false," Stang's niece, Angela Mason, told The Associated Press. "She was the happiest person. She needed nothing, she just loved the people down there."
The early morning attack came less than a week after she met with Human Rights Secretary Nilmario Miranda to report that four local farmers had received death threats. It was not immediately clear when that meeting occurred.
"This is extremely serious," Miranda told reporters on Saturday. "We cannot allow this murder to go unpunished."
Brazilian President Luiz Inacio Lula da Silva ordered federal police to conduct a thorough investigation into Stang's murder. About 15 federal officers were immediately dispatched to the crime scene, police said.
Miranda and Environment Minister Marina Silva were sent to Anapu to track the investigation.
The Catholic Church's Land Pastoral in Brazil on Saturday issued a statement condemning the incident, calling it an "assassination."
Mason said the family was shocked by her aunt's death, but that Stang had told them for some time that there was a bounty on her.
"She had told us there was a price on her head. People were hired to kill her," Mason said.
Stang was a member of the Congregation of the Sisters of Notre Dame de Namur, an international Catholic religious order.
Last June, Stang was honoured by the state of Para for her work in the Amazon region. In December she also received an award from the Brazilian Bar Association for her work helping the local rural workers.