Federal deputy Jair Bolsonaro delivers a speech during the national convention of the Party for Socialism and Liberation (PSL) where he is to be formalised as a candidate for the Presidency of the Republic, in Rio de Janeiro, Brazil July 22, 2018.

Brazilian President Jair Bolsonaro claimed on Friday that Hollywood star Leonardo DiCaprio financed fires being set in the Amazon rainforest, without presenting any evidence, the right-wing leader's latest broadside in casting blame over forest fires that have generated international concern.

Bolsonaro appeared to be commenting on social media postings claiming that the environmental organization the World Wildlife Fund (WWF) had paid for images taken by volunteer firefighters that it then supposedly used to solicit donations, including a $500,000 contribution from DiCaprio.

The WWF has denied receiving a donation from DiCaprio or obtaining photos from the firefighters.

"This Leonardo DiCaprio is a cool guy, right? Giving money to torch the Amazon," Bolsonaro said on Friday during brief remarks in front of the presidential residence.

DiCaprio denied having donated to the WWF. In a statement, the actor lauded "the people of Brazil working to save their natural and cultural heritage." But, he said, "While worthy of support, we did not fund the organizations targeted."

DiCaprio has been an outspoken advocate on behalf of combating climate change, speaking frequently about environmental issues including the Amazon forest fires. His Leonardo DiCaprio Foundation, which is focused on projects that "protect vulnerable wildlife from extinction," is part of the Earth Alliance.

Four members of the nongovernmental organization Alter do Chão Fire Brigade were arrested on Tuesday with police accusing them of purposefully setting fires in order to document them and drum up more donations. They were released on Thursday on a judge's order.

Politicians and other NGOs fiercely criticized the arrest, saying it was part of a concerted attempt by Bolsonaro's government to harass environmental groups.

Scientists and activists blame land speculators, farmers and ranchers for setting the fires to clear land for agricultural use, saying that deforesters are being emboldened by Bolsonaro's rhetoric of promoting development and farming over preservation.