Brazil's President Jair Bolsonaro vowed Monday to defend his controversial Amazon policy at this month's UN General Assembly even if he had to do so "in a wheelchair."

"I will appear before the UN even in a wheelchair, on a stretcher. I will appear because I want to talk about the Amazon," Bolsonaro told reporters outside his official residence in Brasilia.

Bolsonaro is due to undergo surgery next Sunday to correct an incisional hernia, his fourth operation since he was stabbed nearly a year ago during the presidential campaign.

Doctors said Bolsonaro would need 10 days' rest following the operation, which would be performed in Sao Paulo at the Hospital Vila Sur.

Brazil traditionally makes the first speech at the General Assembly meeting, set for September 24.

The far-right president has been widely criticized over his support for Amazon deforestation and a delayed reaction to thousands of wildfires which have devastated vast areas of the rainforest.

Bolsonaro has accused France and Germany of "buying" Brazil's sovereignty after the G7 group of rich democracies offered $20 million in Amazon fire aid. He initially rejected the money unless his French counterpart Emmanuel Macron withdrew "insults" made against him.