Illegal loggers are ramping up a “brutal, fast” assault on the Brazilian Amazon with the blessing of the far-right president Jair Bolsonaro, the sacked head of the government agency tasked with monitoring deforestation has warned.

Speaking to the Guardian five days after his dismissal, Ricardo Galvão said he was “praying to the heavens” the far-right leader would change tack before the Amazon – and Brazil’s international reputation as an environmental leader – were ruined.

“What is happening is that this government has sent a clear message that there will not be any more punishment [for environmental crimes] like before … This government is sending a very clear message that the control of deforestation will not be like it was in the past …. And when the loggers hear this message that they will no longer be supervised as they were in the past, they penetrate [the rainforest],” Galvão said, claiming “enormous” damage had already been done since Bolsonaro took power in January.

“It is a question of brutal, fast economic exploitation.”

Galvão, an internationally respected scientist, was director of Brazil’s National Institute for Space Research (Inpe) until last week when a public clash with Bolsonaro cost him his job.

Days earlier, during a meeting with foreign journalists, Bolsonaro had publicly questioned Inpe’s data suggesting an alarming spike in Amazon destruction and accused Galvão of peddling “lies”.

That attack lead the MIT-trained physicist to hit back at his “pusillanimous” president.

“I felt great indignation and great sadness,” the 71-year-old scientist recalled of what he called Bolsonaro’s “infantile” attack on Inpe and its staff.

In an interview with the Guardian, Galvão accused Bolsonaro and two cabinet members – the environment minister, Ricardo Salles, and the institutional security chief, General Augusto Heleno – of waging a months-long battle to undermine his agency, which uses satellite and radar technology to observe and help prevent deforestation.

Galvão claimed the campaign was designed to discredit Inpe’s findings and thus clear the way for greater exploitation of the Amazon.

“There is no doubt about it. They have much closer relations with the loggers [than previous governments] … The president has said explicitly that he wants to make deals with American companies to exploit minerals in indigenous reserves,” Galvão said.

“It is a negative plan with the intention of reducing control over the Amazon … because they believe that by exploiting the Amazon they will achieve much faster economic development of the region … This is completely mistaken,” the scientist added.

Already, in the first seven months of his four-year term, Bolsonaro had helped cause “an enormous increase” in deforestation by signalling leniency towards those wrecking the rainforest, Galvão claimed.

Environmentalists and scientists from around the world have condemned Galvão’s sacking which some suspect is designed to cover up inconvenient truths about the obliteration of vast tracts of jungle under Bolsonaro.

Nasa scientist Douglas Morton, who has collaborated with Inpe for nearly two decades, said its highly-trained scientists deserved to be “lauded” for their “pioneering, rigorous and robust” research which had brought great benefits to Brazil and its environment. He called Bolsonaro’s move “concerning”.

Romulo Batista, a Greenpeace campaigner in Brazil, said Galvão’s dismissal reflected Bolsonaro’s hostility to science and the environment. “This is not a government that is based on facts … this is a government whose modus operandi is the lie,” Batista said.

But Batista said Bolsonaro would fail to suppress the truth about the accelerating assault on the Amazon.

“If he thinks that by sacking an internationally renowned scientist … and bringing in someone who is going to hide or distort or introduce data that is not true he will manage to convey the false impression that Amazon deforestation is under control, he is very mistaken. There are numerous other [monitoring] systems that will show the truth.”

After nearly five decades serving his country, Galvão said he felt sadness at the circumstances surrounding his sacking and the plight of Brazil’s environment. “The country is seeing a political scenario that is going to cause great damage in the future.”

Galvão echoed fears over research suggesting deforestation was pushing the world’s biggest rainforest towards a catastrophic tipping point from which it would not recover. “This is a very great danger – not to mention that the Amazon is essential to control the rain cycles across South America.”

Galvão also accused Bolsonaro of dismantling Brazil’s hard-earned reputation as a environmental leader – a reputation his agency helped cement by producing deforestation alerts that helped authorities slash Amazon destruction between 2004 and 2012.

“Brazil was seen in a very positive light as a world leader on environmental preservation. This is being rapidly destroyed by the Bolsonaro government,” he said.

Galvão said he hoped the international community would now support “those Brazilians who are struggling against this state of affairs, and force the government to understand that increasing deforestation in the Amazon will only cause harm to Brazil – and to the government itself”.

“I hope, and I pray to the heavens, that the president changes his stance and returns to the correct policy Brazil adopted in the past,” he added.

That seems unlikely. This week, as new Inpe data emerged suggesting an “explosion” of Amazon deforestation in July, Bolsonaro scoffed at his portrayal as Brazil’s “Captain Chainsaw” and mocked Emmanuel Macron and Angela Merkel for challenging him on the environment.

To hoots of approval from his audience, Bolsonaro declared: “They still haven’t realized Brazil’s under new management.”