Daniel Wilkinson, managing director of Human Rights Watch's Americas division, says President Jair Bolsonaro has put "defenders of the [Amazon] forest at serious risk."
Marcelo Crivella, the mayor of Rio de Janeiro, says 11 people died after a fire ripped through Badim Hospital.
Trump aide says US is keen to tackle blazes engulfing parts of the world's largest rainforest but it prefers a plan that includes a discussion with Brazil's government.
The announcement suggests Bolsonaro has dropped an earlier demand that French President Emmanuel Macron withdraw "insults" made against him before he would accept a G7 offer to help put out the fires in the world's largest rainforest.
G7 countries pledged $20 million to fight the blaze destroying the world's largest rainforest at the Biarritz summit hosted by French President Macron, who insisted the Amazon should be discussed as a top priority.
UK PM Boris Johnson pledged $12.3 million to help restore the Amazon which has been ravaged by fires. Brazilian warplanes have been dumping water on the blaze in Rondonia, after a global outcry over the destruction of the world's largest rainforest.
Iranian Foreign Minister Mohammad Javad Zarif's presence had not been announced and represented a gamble by French host Emmanuel Macron who is seeking to soothe spiralling tensions between Iran and the US.
Some 44,000 troops will be available for "unprecedented" operations to put out the fires, and forces are heading to six Brazilian states that asked for federal help.
Against the global chorus of condemnation, Brazilian President Jair Bolsonaro has been mobilising the army to help combat the blazes, while his administration launched a diplomatic charm offensive to try to mend bridges.
Over 70,000 fires have taken place in just Brazil this year, the consequences of which will affect humanity for generations.
Paris and the UN called for the protection of the fire-plagued Amazon rainforest as Brazil's right-wing president accused his French counterpart of having a "colonialist mentality" over the issue.
Norway and Germany, among others, have discontinued financial aid for the Amazon Fund, leading some Brazilian federal governors to appeal directly to Europe to change their minds.
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