And he again suggested that non-governmental organisations had started fires in the rainforest, but admitted he had no evidence for this claim.
He added that his government was investigating the fires.
Earlier, Brazil’s Environment Minister Ricardo Salles was heckled at a meeting on climate change.
Conservationists have blamed Brazil’s government for the Amazon’s plight.
They say Mr Bolsonaro has encouraged the clearing of land by loggers and farmers, thereby speeding up the deforestation of the rainforest.
Satellite data published by the National Institute for Space research (Inpe) shows an increase of 85% this year in fires across Brazil, most of them in the Amazon region.
The largest rainforest in the world, the Amazon is a vital carbon store that slows down the pace of global warming.
Answering questions from reporters on Thursday, Mr Bolsonaro said the government couldn’t simply get the ministry of the interior to send 40 men to fight a fire.
“Forty men to fight a fire? There aren’t the resources. This chaos has arrived,” he said.
On Wednesday, the president had suggested that non-governmental organisations (NGOs) could have started fires as revenge for his government slashing their funding.
Asked on Thursday who was responsible for starting the fires, he responded: “The Indians, do you want me to blame the Indians? Do you want me to blame the Martians?… Everyone is a suspect, but the biggest suspects are NGOs.”
Asked if there was any proof of this, he replied: “Did I accuse NGOs directly? I just said I suspect them.”
President Bolsonaro has further angered those concerned over the spike in fires by brushing off the latest data.
He argued that it was the season of the “queimada”, when farmers burn land to clear it before planting but Inpe has noted that the number of fires is not in line with those normally reported during the dry season.
It is not the first time Mr Bolsonaro has cast doubt on figures suggesting that the Amazon is deteriorating rapidly.
Last month, he accused Inpe’s director of lying about the scale of deforestation and trying to undermine the government. It came after Inpe published data showing an 88% increase in deforestation in the Amazon in June compared to the same month a year ago.
The director of the agency later announced that he was being sacked amid the row.
What happened to Ricardo Salles?
As the minister took to the stage at the Latin American and Caribbean Climate Week in the Brazilian city of Salvador, some of those present shouted “the Amazon region is burning”.
As soon as his name was announced, most of those attending the opening session of the plenary booed and shouted, with only a few people clapping.
The conference, organised by the United Nations, aims to promote action on climate change in the region.
It is being attended by representatives from non-governmental organisations, businesses and educational organisations, among others.
What are people upset about?
Climate activists and conservationists have been scathing about the Bolsonaro government and its policies, which favour development over conservation.
They say that since President Bolsonaro took office, the Amazon rainforest has suffered losses at an accelerated rate.
Their anger was further fuelled by satellite data showing a steep rise in fires in the Amazon region this year.
The figures suggest there have been more than 75,000 fires so far this year for the whole of Brazil, compared with just over 40,000 over the same period in 2018.