A British journalist and a Brazilian Indigenous expert have gone missing in a remote and dangerous part of the Amazon rainforest that is home to the world's largest population of uncontacted tribes.
An association representing the region's Indigenous peoples said Dom Phillips and Bruno Araújo Pereira had been threatened during a two-day reporting trip to the Javari Valley, in western Brazil near the country's border with Peru.
Brazil's navy has sent a search and rescue team to look for the pair and authorities are investigating their disappearance.
Who are the two men missing in the Amazon?
Mr Phillips, 57, is a British freelance journalist who has written for The Guardian, The Washington Post, The New York Times and other outlets.
He has written extensively about the Amazon and is currently writing a book about the rainforest's preservation with support from the Alicia Patterson Foundation, which awarded him a year-long fellowship for environmental reporting.
He has lived in Brazil for more than a decade and currently lives in Salvador in the state of Bahia.
Mr Pereira is one of Brazil's most knowledgeable experts on isolated and uncontacted tribes.
He is a previous advisor for the Union of Indigenous Peoples of the Javari Valley (UNIVAJA) and is currently on leave from a post with Brazil's Indigenous affairs agency.
The men disappeared while returning from their reporting trip in the Javari Valley, in Brazil's Amazonas state.
They were last seen at 7am on Sunday in the Sao Rafael community.
They were expected to travel from the area to the city of Atalaia do Norte, about an hour away, on a small boat, but did not show up.
The UNIVAJA said the two men were the only two people who would have been travelling on the boat.
What's the Javari Valley? Is it dangerous?
The Javari Valley or Vale do Javari is a region about the size of Ireland which is home to the highest number of uncontacted Indigenous people in the world.
Several thousand Indigenous people live in the area in dozens of villages.
The area is under threat from a range of groups, including illegal miners, loggers, hunters and groups that grow coca, the plants that provide the raw material for cocaine.
It has been the site of multiple shootouts between hunters, fishers and government agents and is also a major route for the smuggling of cocaine from Peru into Brazil.
Journalists from regional media outlets have been murdered in the Amazon in recent years and reports of threats against reporters have resulted in limited access to some areas dominated by criminal activity.
Were there any warnings? Were the pair threatened?
UNIVAJA has said Mr Phillips and Mr Pereira received threats in recent days, but it isn't yet clear what kind of threats were made against them.
Mr Pereira has previously been threatened by illegal fishermen and poachers and is in the habit of carrying a gun.
Survival International, an NGO responsible for defending tribal peoples, said threats had been directed at Mr Pereira because of his years of work with Indigenous tribes.
They said those threats "[make] the need for immediate action to locate him and Dom all the more pressing".
Who's looking for them?
Brazil's federal police, Amazonas state civil police, the national guard and the navy have all been mobilised to search for the men, with the effort to be coordinated by the navy.
The navy's 10-person search and rescue team is expected to arrive at Atalaia do Norte around 7pm local time before heading to the area the pair were last seen.
The UNIVAJA has also dispatched two search parties to look for the men.
However, federal police have said there is no information at the moment on their whereabouts or even a theory about what might have happened.
