Four anti-logging activists have been slain in Peru, officials have said.
The four men, who belonged to the Ashaninka community, were on their way to Brazil to attend a meeting on how to prevent illegal logging in Peru.
According to other activists, the men had received several death threats from illegal loggers, who are believed to be behind the murders.
One of the victims was well-known activist Edwin Chota, often featured in the media for his attempts to protect his community from illegal logging.
"He [Chota] threatened to upset the status quo," David Salisbury, a professor at the US University of Richmond told news agency AP. "The illegal loggers are on record for wanting Edwin dead."
More than 900 environmental activists have been slain in 35 countries over the past decade, according to a survey by London-based Global Witness group, which reports on links between environmental exploitation and human rights abuses.
The survey said Brazil is the world's most dangerous place for environmental activists with 448 deaths between 2002 and 2013, followed by 109 in Honduras and 58 in Peru.
According to a 2012 study by the World Bank, as much as 80% of Peru's timber exports derives from illegal logging.
Last July, Brazil's National Indian Foundation (Funai) caught on video the encounter of a previously uncontacted tribe with people from the outside world.
The men were believed to be part of the Rio Xinane tribe and to have fled Peru to escape from illegal logging and drug trafficking.