Brazilian authorities on Wednesday arrested a man in connection with the disappearance of a British journalist and a local indigenous expert in the Amazon, police said, as calls mounted for officials to deliver answers on what happened to them.

As the search approached its fifth day, official information was scarce on the investigation into the fate of Dom Phillips, 57, and Bruno Pereira, 41, who disappeared early Sunday in the remote, jungle-covered Javari Valley in Brazil, near the border with Peru.

Brazilian police and military officers told a news conference they had questioned six people and arrested one. But they said it was unclear whether the suspect was directly linked to the case.

In the meantime, the authorities are pursuing "all lines of investigation," and still hope to find the men alive, said lead investigator Alexandre Fontes.

Investigators said the arrested man was detained during a random stop-and-search operation in the region, when officers found him with drugs and illegally carrying 7.62-millimeter ammunition -- a round typically used in assault rifles.

Witnesses reportedly saw the man 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.

But "we have not established any connection between him and the (disappearance) for now," the Amazonas state security secretary, General Carlos Alberto Mansur, told reporters.

Local indigenous activists say Phillips and Pereira received threats last week while working in the region, which has seen a surge of invasions of protected indigenous lands for illegal fishing, logging, gold mining and drug trafficking.

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 such invasions, including by helping indigenous communities set up their own patrols.

Investigators insisted they were doing their best in what Fontes called a "very complicated region," criss-crossed by meandering rivers and reachable only by helicopter, small plane or boat.

Veteran foreign correspondent Dom Phillips (C) takes notes as he talks with indigenous people in the Brazilian Amazon in 2019
Veteran foreign correspondent Dom Phillips (C) takes notes as he talks with indigenous people in the Brazilian Amazon in 2019 AFP / Joao LAET

A total of 250 officers are working on the rescue mission, including jungle operations experts sent by the army and rescue divers trained to work in murky waters, supported by two helicopters, three drones and 16 boats, they said.

Pressure has been mounting on President Jair Bolsonaro's government, which faces accusations of failing to scale up the search fast enough in the far-flung region.

"We have reinforced the search operation since yesterday," Justice Minister Anderson Torres wrote on Twitter.

The case has drawn urgent appeals from leading media organizations and environmental and human-rights groups -- joined by a growing list of high-profile figures including football legend Pele and current star Richarlison.

"The fight for the preservation of the Amazon Forest and the protection of indigenous groups belongs to all of us," Pele posted on Instagram, along with a video from Tuesday of Phillips's distraught wife choking back sobs as she pleaded with the Brazilian authorities to help.

"I join the many voices that make the appeal to intensify the search and to find them as soon as possible," added the 81-year-old footballer, considered by many the greatest of all time.

Brazil and Everton striker Richarlison tweeted the same video.

"I ask the authorities, please, act urgently and do everything possible to find Dom Phillips and Bruno Pereira!" he wrote.

The plea also reached the Summit of the Americas in Los Angeles, where US President Joe Biden is meeting regional leaders this week, including a sit-down with Bolsonaro Thursday.

Activists mounted a giant screen on a truck that stopped at various landmarks, including the iconic Hollywood sign, with the message: "Where are Dom & Bruno?"