Brazilian authorities said Wednesday they have detained a suspect in the case of a missing British journalist and indigenous affairs expert -- but are yet to establish whether the man was linked to their disappearance in a remote region of the Amazon.

Concerns are growing over the fate of Dom Phillips and Bruno Araújo Pereira, who were first reported missing in the Javari Valley, in the far western part of Amazonas state on Sunday. They had reportedly received death threats just days prior.

In a news conference Wednesday, Amazonas state security Secretary General Carlos Alberto Mansur said the suspect remains under investigation in police custody.

Mansur said the man was arrested after being found in possession of "a lot of drugs" and ammunition used for illegal hunting.

Authorities said Wednesday they were pursuing several lines of investigation, including homicide, and added they still "can't rule out anything.”

Gen. Placido (center) speaks between Eduardo Alexandre Fontes (right), Regional Superintendent of Amazonas State Federal Police and Col. Muniz during a news conference in Manaus, Brazil, on Wednesday.

Mansur noted that five other people have also been questioned by police in connection with the disappearance of Phillips and Pereira, who had traveled to the region to conduct research for a book project on conservation efforts in the region.

Ahead of the news conference, media organizations and family members of both missing men called for the federal government to step up their search efforts. Federal Police Superintendent Eduardo Alexandre Fontes said Wednesday that a total of 250 men, two helicopters, three drones and 16 boats have been deployed for the search and rescue operation.

Phillips and Pereira have been missing for more than 72 hours, according to the Coordination of the Indigenous Organization. The organization, known as UNIVAJA, said satellite information showed the pair's last known location in the São Rafael community early on Sunday morning, where they were expected to meet a local leader who never showed up.

A “dangerous” region

Home to thousands of indigenous people and about 16 un-contacted groups, the Javari Valley -- the second largest indigenous territory in Brazil -- is a patchwork of rivers and dense forest that makes access very difficult. The area has come under increased threat from illegal miners, loggers, hunters and international drug traffickers exploiting its vast network of rivers.

On Wednesday, Federal Police Superintendent Fontes described the area where Phillips and Pereira went missing as "complicated” and “dangerous.”

Phillips and Pereira had traveled to the region to conduct research for a book on conservation efforts there. Phillips, an Amazon specialist, had previously reported for British newspaper The Guardian on threats posed by illegal mining and cattle ranchers to un-contacted indigenous groups in the region.

Despite being under government protection, the Javari Valley can be a hostile environment for journalists and indigenous rights activists. According to Brazil's Public Prosecutor's Office, an indigenous affairs worker was murdered in the area in September 2019.

“In this region, violence is advancing in an increasingly uncontrolled manner in the context of the invasion of indigenous lands and lands that belong to the state, repression of the freedom of press and the work of journalists,” UNIVAJA said in a statement.

In 2018, Phillips reported on the threats posed by illegal mining and cattle ranchers to uncontacted indigenous groups there, with Pereira at the heart of that article.

Survival International, an NGO that advocates for indigenous peoples, said Pereira had previously received “many threats” as a result of his work as an “ally of the Indigenous struggle.” (CNN)

•PHOTO: British journalist Dom Phillips (pictured) and indigenous affairs expert Bruno Araújo Pereira were reported missing in a remote part of the Brazilian Amazon on Sunday.