A boat speeds on the Jurura river in the Brazilian Amazon forest on March 15. Photo: AFP

Rights groups and families of a British journalist and Brazilian Indigenous expert who went missing deep in the Amazon after receiving threats pleaded Tuesday for authorities to accelerate the search operation.

Veteran freelance journalist Dom Phillips, 57, and respected Indigenous specialist Bruno Pereira, 41, went missing early Sunday while traveling by boat in Brazil's Javari Valley, near the border with Peru, where Phillips was researching a book.

As the 48-hour mark passed, speculation swirled around whether they could have fallen victims to an accident or foul play.

As of Tuesday night, authorities had no reports on their whereabouts but Amazonas state civil police said they were questioning a "suspect" and that four other people had testified as "witnesses," though no arrests were made.

Local Indigenous activists said the pair received threats last week for their work in the remote region, which has seen a surge of illegal logging, gold mining, poaching and drug trafficking.

Loved ones were holding out hope the pair would be found.

"I want to make an appeal to the government to intensify the search," Phillips's Brazilian wife, Alessandra Sampaio, said in a video message.

The Brazilian government expressed its "grave concern," and said police were taking "all possible measures to find [the men] as quickly as possible."

But the authorities faced accusations of failing to act urgently enough.

AFP