Authorities combing a remote corner of the Amazon for a missing British journalist and Brazilian indigenous expert are investigating possible human remains and a spot where something appears to have been buried, officials said Friday.

Fears have been mounting over the fate of Dom Phillips, 57, a veteran contributor to The Guardian newspaper, and Bruno Pereira, 41, a respected specialist in indigenous peoples, since they disappeared Sunday after receiving threats during a research trip to Brazil's Javari Valley, a far-flung jungle region that has seen a surge of illegal fishing, logging, mining and drug trafficking.

Authorities have arrested a suspect named as 41-year-old Amarildo da Costa de Oliveira, nicknamed "Pelado," who witnesses say pursued the men upriver. A blood spot found on a tarp in his boat has been sent for analysis at the crime lab in Manaus, the capital of Amazonas state.

A search boat looks for signs of British journalist Dom Phillips and Brazilian indigenous expert Bruno Pereira on the Itaguai river
A search boat looks for signs of British journalist Dom Phillips and Brazilian indigenous expert Bruno Pereira on the Itaguai river AFP / Joao Laet

Emergency official Geonivan Maciel said investigators now had a new lead in the case: a suspicious site with "overturned earth" in a community called Cachoeira, on a bank of the Itaquai river, where the men were last seen.

"It's as if someone had dug something at the site, buried something there," Maciel told journalists accompanying the search.

"We're going to carry out a scan of the bottom to verify... We can't say there's definite evidence, but we're going to see if there's something there that could identify something about the two missing men."

Demonstrators from the National Indigenous Foundation highlight the disappearance of British journalist Dom Phillips and Brazilian Indigenous affairs specialist Bruno Pereira, in Brasilia on June 9, 2022
Demonstrators from the National Indigenous Foundation highlight the disappearance of British journalist Dom Phillips and Brazilian Indigenous affairs specialist Bruno Pereira, in Brasilia on June 9, 2022 AFP / EVARISTO SA

Federal police later said in a statement investigators had found "apparently human organic material" during their search.

It was unclear whether it came from the same site.

Investigators collected genetic material from Phillips's and Pereira's homes for comparison, the statement said.

A police boat patrols in Atalaia do Norte searching for missing Indigenous expert Bruno Pereira and journalist Dom Phillips on June 10, 2022
A police boat patrols in Atalaia do Norte searching for missing Indigenous expert Bruno Pereira and journalist Dom Phillips on June 10, 2022 AFP / JOÃO LAET

President Jair Bolsonaro's government has faced accusations of failing to scale up the search operation fast enough.

And Bolsonaro himself came in for criticism when he appeared to blame the men, saying they had gone on an "unadvisable adventure."

Veteran foreign correspondent Dom Phillips talks to two men in Roraima State, Brazil in November 2019
Veteran foreign correspondent Dom Phillips talks to two men in Roraima State, Brazil in November 2019 AFP / Joao LAET

The government faces mounting pressure over the case from high-profile media organizations, rights groups and celebrities including football legend Pele and iconic singer Caetano Veloso.

Environmental group Greenpeace fired a new salvo Friday, calling the men's disappearance "the tip of the iceberg of the policy of extermination pushed by the current administration."

Bolsonaro, who has pushed to open protected indigenous lands to mining, has presided over a surge of destruction in the Amazon, a key resource in the race to curb climate change.

Since the far-right president took office in 2019, average annual deforestation in the Brazilian Amazon has risen by 75 percent from the previous decade.

"The extreme violence and insecurity in the Javari Valley is a reflection of the absence of competent and effective action by the Brazilian government across the Amazon," Greenpeace said in a statement.

Police have said they are hopeful of finding the pair alive but are not ruling out any possibility, including homicide.

Witnesses say they saw "Pelado" trailing Phillips and Pereira's boat as the pair made their way back to the small city of Atalaia do Norte after a research trip to an area known as Jaburu lake.

The suspect was arrested with drugs and unlicensed ammunition of a caliber often used in assault rifles.

Local indigenous activists say Phillips and Pereira received threats last week while working in the region.

Pereira, a highly regarded expert on the region currently on leave from Brazilian indigenous affairs agency FUNAI, has been a target of death threats for his work fighting illegal invasions of indigenous lands.

Phillips was accompanying him for a book project on sustainable development in the Amazon.