Brazil says it is stepping up its search for British journalist Dom Phillips, 57, and Brazilian indigenous expert Bruno Pereira, 41, after it was criticised for its slow response to their disappearance.

The two men went missing in the rainforest near Brazil's border with Peru on Sunday.

No trace has been found of them or the boat they were travelling in.

The lead investigator said his team was "pursuing all lines of inquiry".

There has been huge concern for the welfare of the men after it emerged that Mr Pereira had received death threats in the week before they went missing.

Brazilian football legend Pelé is among those who have urged the authorities to intensify to scale up their search.

He retweeted a video in which Mr Phillip's wife, Alessandra Sampaio, said she hoped that "the love of my life" would be found alive.

Investigators said there were now 250 members of the security forces taking part in the search, up from just about a dozen in the first days.

They said the team included divers and experts in jungle terrain. Two helicopters, more than a dozen boats and drones are also being used.

Six people have been questioned in connection with the men's disappearance, but police said only one had been arrested while the others were questioned as witnesses.

They said that the arrested man had been detained during a random stop-and-search operation in the area during which he had been found illegally carrying ammunition.

A local security official said that "we have not established any connection between him and the [disappearance] for now".

Lead investigator Alexandre Fontes described the area as a "very complicated region" which he said could only be reached by helicopter, small plane or boat.

Indigenous rights groups which Mr Pereira worked with were the first to raise the alarm about the disappearance of the expert on isolated indigenous groups and the journalist.

They said that Mr Pereira had received threatening letters over his work fighting against illegal fishing in the area.

Both Mr Pereira and Mr Phillips, who has written about threats to the Amazon for publications such as The Guardian and the Washington Post, are hugely experienced and planned their journeys thoroughly. They had a new boat and plenty of fuel, the rights group said.

The area where they disappeared is home to around 6,300 indigenous people from more than 20 groups.

As well as clashes with fishermen catching protected stock, it has also seen incursions by illegal gold miners, loggers and drug traffickers who smuggle cocaine from neighbouring Peru.

Both Mr Pereira, who has worked for the government's indigenous affairs agency Funai, and Mr Phillips, who was carrying out research for a book on the Amazon, documented these threats as part of their work.

Brazil's president, Jair Bolsonaro, has come under fire for referring to the work of the two men as an "adventure" and appeared to blame them for their disappearance.

"Two people in a boat in a region like that, completely wild - it's an unadvisable adventure. Anything can happen," he said on Tuesday.