The headquarters of an award-winning Brazilian NGO that works with remote communities in the Amazon has been raided by police, who also arrested four volunteer firefighters and accused them of starting wildfires to raise international funding.

At dawn on Tuesday, heavily armed police raided the offices of the Health and Happiness Project, (known by its Portuguese initials PSA) in Alter do Chão in the Amazon state of Pará, seizing computers and documents.

PSA has close links to the Alter do Chão volunteer fire brigade, which in September helped battle huge wildfires raging through protected areas in this popular tourist region. The four arrested firefighters were members of the volunteer brigade, and one of them works for PSA.

The arrests came three months after Brazil’s far-right president Jair Bolsonaro sought to blame a surge in Amazon fires on NGOs, without providing any evidence.

“It is a Kafkaesque situation. We were all taken by surprise without understanding why,” said the Health and Happiness Project’s coordinator Caetano Scannavino. “If [the firefighters] were really criminals they must be Hollywood actors because they tricked us.”

The Alter do Chão fire brigade also denied the accusations. “We are sure that whatever the accusation, their innocence will be made clear,” it said in a statement.

Local indigenous associations and campaigners said the raid and arrests were a politically motivated attack on dedicated firefighters and a respected NGO.

“This is a very serious NGO whose work is recognised by the local population and internationally,” said Felipe Milanez, a professor of humanities at the Federal University of Bahia.

The Iwipuragã indigenous association said: “We know the serious work and honesty of our firefighters.”

José de Melo Jr, the detective leading the investigation, denied any political dimension and said he had evidence of arson.

“We observed in some images that the firefighters were responsible for starting these fires,” he said. “They created a problem for them to solve and make money from.”

Detective Melo Jr sent the Guardian a video he said firefighters had uploaded to YouTube. Apparently shot from a drone, it showed blazes burning in a stretch of forest before panning back to reveal a vehicle on a dirt road, but did not show anybody lighting any fires.

﻿The Alter do Chão brigade was formed last year and has close links to the Health and Happiness Project, founded in 1987 by Caetano Scannavino’s brother Eugênio, a doctor from São Paulo.

“They have paralysed our operations,” said Eugênio Scannavino. “This is very dangerous. It is a retaliation against the NGOs.”

The NGO’s activities include operating a hospital boat visiting remote riverside communities and helping indigenous communities develop sustainable tourism. It also runs an experimental agroforestry centre.

On Monday the Folha de S.Paulo newspaper reported that real estate interests were putting pressure on protected areas in Alter do Chão. In September federal prosecutors said they suspected one of the Alter do Chão fires had been started in an area invaded by a land grabber on the run from police after being handed a six-year, 10-month prison sentence.

But Detective Melo Jr said his operation has not examined any possible links between the fires and land speculation which locals say is rife on protected areas.﻿