A leading Cambodian environmentalist who investigated illegal logging has been killed in a confrontation with police, officials say.
Chut Wutty was shot dead while travelling in a threatened forest region in the south-west.
Details of the incident are unclear, but police say an officer was also killed in the exchange.
Mr Wutty had been helping indigenous people organise protests against the exploitation of protected forests.
Chut Wutty was driving through a remote area of Koh Kong province with two journalists from the Cambodia Daily newspaper at the time of the incident.
The BBC's Guy De Launey in Phnom Penh says there have been suggestions that military police ordered the reporters to delete images from their cameras and that Mr Wutty objected.
Precisely what happened next is unclear, but shots were fired, and the environmental activist was fatally wounded.
A military police commander said one of his officers was also killed, while "doing his duty".
Mr Wutty was one of the most outspoken activists in Cambodia. One of his colleagues told the BBC that he had angered many influential people.
He had received death threats in the past and sometimes carried an AK-47 rifle in his car.
The campaign group Global Witness says he had been one of the "few remaining Cambodian activists willing to speak out against the rapid escalation of illegal logging and land grabbing".
It says that corruption and violence around Cambodia's forests have been "well documented", and that the killing of Mr Wutty's demonstrates that "those who take on these vested interests face intimidation and even death".
The two journalists travelling with Mr Wutty were initially held by police, but they have now been released.
The local UN Human Rights office is investigating the incident.