Veteran foreign correspondent Dom Phillips, 57, went missing while researching a book in the Brazilian Amazon's Javari Valley with respected indigenous expert Bruno Pereira, said The Guardian newspaper, where Phillips has been a longtime contributor.
The pair had traveled by boat to Jaburu lake, in the northern state of Amazonas near Brazil's border with Peru, and were expected to return to the city of Atalaia do Norte by around 9:00 am Sunday, two rights groups said in a statement.
The men had "received threats in the field" last week, said the groups, the Union of Indigenous Organizations of the Javari Valley (UNIVAJA) and the Observatory for the Human Rights of Isolated and Recently Contacted Indigenous Peoples (OPI).
They did not give further details, but Pereira, an expert at Brazil's indigenous affairs agency FUNAI with deep knowledge of the region, has regularly received threats from loggers and miners trying to invade isolated indigenous groups' land.
FUNAI told AFP it was collaborating with local authorities on the search effort. It added that Pereira was on leave from the agency "to pursue personal interests."
Phillips and Pereira had traveled to the region around a FUNAI monitoring base, and reached Jaburu lake Friday evening, UNIVAJA and OPI said.
Related:
Amazon rainforest: 2020-09-15 Protector of Brazil's Indigenous Groups Fatally Shot With Arrow by Isolated Tribe
Amazon rainforest: 2020-03-30 Virus Has Exposed Modern Americans' Disconnect from Reality
Amazon rainforest: 2019-10-10 Teenage Climate Activist Greta Thunberg Named Nobel Peace Prize Favourite
Amazon rainforest: 2020-09-15 Protector of Brazil's Indigenous Groups Fatally Shot With Arrow by Isolated Tribe
Amazon rainforest: 2020-03-30 Virus Has Exposed Modern Americans' Disconnect from Reality
Amazon rainforest: 2019-10-10 Teenage Climate Activist Greta Thunberg Named Nobel Peace Prize Favourite