Fears are growing over the safety of a British journalist and a Brazilian Indigenous expert who have disappeared in one of the remotest corners of the Amazon just days after receiving threats. Dom Phillips, a longtime contributor to the Guardian in Brazil, was last seen over the weekend in the Javari region of Amazonas state – a vast region of rivers and rainforests near the border with Peru. The reporter was traveling with Bruno Araújo Pereira, a former government official tasked with protecting Brazil’s uncontacted tribes, who has long received threats from the loggers and miners seeking to invade their lands. Phillips, 57, who is working on a book about the environment with support from the Alicia Patterson Foundation, is based in the Brazilian city of Salvador and has been reporting on Brazil for more than 15 years for newspapers including the Guardian, the Washington Post, the New York Times and the Financial Times. On Monday local Indigenous leaders sounded the alarm after the two men vanished during a reporting mission into the network of rivers around the town of Atalaia do Norte, the entry point into the Javari reserve. In a statement, the Indigenous group Univaja said Phillips and Pereira had set off last week by boat for a region known as the Lago do Jaburu, reaching their destination on Friday evening. At about 6am on Sunday, after two days in the field, the pair are thought to have started returning by river to Atalaia do Norte. The journey should have taken no more than three hours but a search party was sent out at about 2pm after they failed to arrive. “We need an urgent search mission. We need the police, we need the army, we need firefighters, we need civil defense forces. We have no time to lose,” said Beto Marubo, a prominent Indigenous leader from the region who knows both of the missing men. A spokesperson for Guardian News & Media said: “The Guardian is very concerned and is urgently seeking information about Mr Phillips’ whereabouts and condition. We are in contact with the British embassy in Brazil and local and national authorities to try to establish the facts as soon as possible.” Phillips had joined one of Pereira’s expeditions to the same region in 2018 to report on the lost tribes of the Amazon for the Guardian. He is known for his love of the Amazon region and has travelled there extensively to report on the crisis facing Brazil’s environment and its Indigenous communities. “Amazônia sua linda (Amazonia you beauty),” the journalist wrote last week on Instagram alongside a video of a boat meandering down one of the region’s rivers. Federal police officials in the capital of Amazonas, Manaus, said they were aware of the disappearances and were working on the case. The navy said it had sent a 10-person crew to the men’s last known location but a spokesperson for the Amazon Military Command said the army had yet to receive orders from Brasília to join the hunt. “We have been informed of the occurrence ... and we are waiting to be actioned by one of the relevant ministries ... so that if we are actioned, we are ready to carry out this humanitarian search and rescue mission in the Javari valley region.” Independent search parties were also being organized by indigenous and environmental activists. Human Rights Watch said it was extremely concerned about the situation and urged authorities to throw every possible resource into the search effort in order to ensure their safety. Brazil’s former president Luiz Inácio Lula da Silva tweeted his concern for the pair. “Phillips interviewed me for the Guardian in 2017. I hope they are found quickly and that they are safe and well,” Lula wrote. Marubo said the Javari region, a vast expanse of jungle which is home to more than 20 Indigenous groups, had grown increasingly tense and perilous in recent years – particularly after the 2019 murder of an indigenous protection official called Maxciel Pereira dos Santos. “Under the Bolsonaro government the pressure has increased even more because the invaders felt empowered and became more aggressive,” added Marubo who said “systematically organized gangs” of illegal miners and hunters were “plundering” the region’s forests and rivers with impunity. “They are veritable gangs and they are very violent,” the Indigenous leader said. Relatives of Phillips in the UK urged Brazil to act. “We implore the Brazilian authorities to send the national guard, federal police and all the powers at their disposal to find our cherished Dom,” tweeted Paul Sherwood, the partner of the journalist’s sister. “He loves Brazil and has committed his career to coverage of the Amazon rainforest. We understand that time is of the essence so please find our Dom as quickly as possible.”