A British journalist and an Indigenous affairs official are still missing in a remote part of Brazil’s Amazon as authorities say they are expanding search efforts in the area, which has seen violent conflicts between fishermen, poachers and government agents.

Dom Phillips, who has been a regular contributor to The Guardian, and Bruno Araújo Pereira were last seen early on Sunday in the Sao Rafael community, reported the Univaja association of people in the Vale do Javari Indigenous territory, for which Mr Pereira has been an adviser.

The pair were returning by boat from the Vale do Javari and bound for the city of Atalaia do Norte, about an hour away, but never showed up.

Mr Pereira is one of the Brazilian Indigenous affairs agency’s most experienced employees operating in the Vale do Javari area.

He oversaw the agency’s regional office and the co-ordination of isolated Indigenous groups before going on his current leave.

He has received a stream of threats from illegal fishermen and poachers, and usually carries a gun.

Univaja said the two had been threatened during their reporting trip.

On Saturday, while they were camped out, two men travelled by river to the Indigenous territory’s boundary and brandished a firearm at a Unijava patrol, the association’s president, Paulo Marubo, told The Associated Press (AP).

Mr Phillips, who has reported from Brazil for more than a decade, has been working on a book about preservation of the Amazon with support from the Alicia Patterson Foundation, which gave him a year-long fellowship for environmental reporting that ran until January.

The pair disappeared while returning from a two-day trip to the Jaburu Lake region, where Mr Phillips interviewed local Indigenous people, Univaja said.

Only the two were on the boat.

The place where they went missing is the primary access route to and from the Vale do Javari, Brazil’s second-largest Indigenous territory that is bigger than Maine, and where several thousand Indigenous people live in dozens of villages.

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

“He is a cautious journalist, with impressive knowledge of the complexities of the Brazilian environmental crisis,” Margaret Engel, the Alicia Patterson Foundation’s executive director, wrote in an email.

“And he is a beautiful writer and a lovely person. The best of our business.”

Brazil’s federal public prosecutors said in a statement on Monday they had opened an investigation and that the Federal Police, Amazonas state’s civil police, the national guard and navy had been mobilised.

The navy, which prosecutors described as co-ordinating the search, said it sent a search-and-rescue team of seven and would deploy a helicopter on Tuesday.

The army’s footprint and manpower is far greater than the navy’s in the region, and there was no indication from officials on why it was not included in the initial search efforts.

But late on Monday, a spokesman for the army’s Amazon division told AP it had since received orders to deploy a search mission.

Mr Phillips has also contributed to the Washington Post and New York Times.

He currently lives in Salvador, a city in Brazil’s Bahia state, with his wife, Alessandra Sampaio, who shared a series of messages on Twitter through a friend.

“I can only pray that Dom and Bruno are well, somewhere, prevented from continuing on for some mechanical reason, and that all of this becomes just one more story in a life replete with them,” Ms Sampaio wrote.

“I know, however, the moment the Amazon is going through and I know the risks that Dom always denounced.”

The Vale do Javari region has experienced repeated shootouts between hunters, fishermen and official security agents, who have a permanent base in the area, which has the world’s largest population of uncontacted Indigenous people.

It is also a major route for cocaine produced on the Peruvian side of the border, then smuggled into Brazil to supply local cities or to be shipped to Europe.

In September 2019, an employee of the Indigenous affairs agency was shot dead in Tabatinga, the largest city in the region. The crime was never solved.

“It is extremely important that Brazilian authorities dedicate all available and necessary resources to the immediate realisation of searches, in order to guarantee, as soon as possible, the safety of the two men,” Maria Laura Canineau, the director of Human Rights Watch in Brazil, said in a statement on Monday.

Journalists working for regional media outlets in the Amazon have been slain in recent years, though there have been no such cases among journalists from national media nor foreign media.

However, there have been several reports of threats, and the press has limited access to several areas dominated by criminal activity, including illegal mining, land-grabbing and drug trafficking.

“I hope they are found soon, that they are well and safe,” former president Luiz Inácio Lula da Silva posted on Twitter.

President Jair Bolsonaro had not commented by late Monday.