A British journalist and a worker of the National Indigenous Institute of Brazil (FUNAI) were reported missing while visiting the Indigenous land of the Yavari Valley, in the western state of Amazonas.

The disappearances were reported through a press release issued jointly by one of the main Indigenous associations in the region, Unijava, and the Observatory for the Human Rights of Isolated or Recently-contacted Indigenous Peoples (OPI).

Bruno Araujo Pereira and Don Phillips, a journalist working for British newspaper The Guardian, were last seen on Sunday morning, June 5, while traveling by boat through the Javari region of Amazonas state. They were returning from a two-day reporting trip, but did not arrive at a scheduled at the town of Atalaia do Norte.

Pereira, 41, a longtime advocate of the Indigenous tribes in the vast and remote jungle area, had received death threats for his work helping protect Indigenous groups from drug traffickers and illegal miners, loggers and hunters who covet land in a region rich with natural resources.

Phillips, 57, was in the region researching a book on sustainable development. He received a fellowship from the Alicia Patterson Foundation to write the book, and was aiming to finish it by the end of this year, as reported by The Guardian.

Both Unijava and OPI referred to the FUNAI employee, Bruno Araújo Pereira, saying that "although he is part of the FUNAI team, he was not in the region on an institutional mission, as he was on leave to attend to personal matters."

Guilherme Torres, the head of the interior department of Amazonas state’s civil police, said Pereira had recently received a threatening letter from a local fisherman who police are trying to locate.

Phillips has reported from Brazil for more than a decade and was working on a book about preservation of the Amazon with support from the Alicia Patterson Foundation.

“We are indeed working with the hypothesis that a crime might have occurred, but there is another, much larger possibility: that they are lost,” Torres told Reuters.

“Now, our priority is to find them alive, especially in these first hours. In parallel, a criminal probe has been opened to see if there was some crime committed,” he continued.

People from the area say that it is highly unlikely the men would have gotten lost in that area.

The wife of the English journalist, Alessandra Sampaio, appealed to the federal government to speed up the search for him and Pereira.

According to Sampaio, the family has "a little bit of hope" of finding both of them alive and has asked that the search be intensified.

"I would like to appeal to the federal government and to the competent bodies to intensify the search, because we still have a little bit of hope of finding them. Even if I don't find the love of my life alive, they have to be found, please. Intensify the search. I didn't want to talk before because the whole family is very shocked and we don't know how to react. But I am making this appeal, please, to intensify these searches," she said in a video shown by TV Bahia.

As reported by The Guardian, there is considerable anger over the lack of urgency shown by Brazilian authorities, and particularly far-right president, Jair Bolsonaro.

The search has been beset by delays and contradictory statements by Brazilian military officials in charge of the region.