Protesters from climate activist group Extinction Rebellion gathered at the Brazilian embassy in London on Friday to call on Brazilian President Jair Bolsonaro to protect the Amazon rainforest.

Indigenous leaders of the Huni Kuin Kaxinawa group joined protesters chanting outside the embassy.

This came as Bolsonaro said on Friday the army may be enlisted to help combat fires sweeping through the Amazon rainforest, as international condemnation and calls for tough action to quell the unfolding crisis continued to mount.

Fires in the Amazon have surged 83% so far this year compared with the same period a year ago, government figures show, destroying vast swathes of forest considered a vital bulwark against global climate change.

The leaders of Britain and France have added their voices to an international chorus of concern. A spokeswoman for British Prime Minister Boris Johnson said he was "deeply concerned" about the fires and "the impact of the tragic loss of these precious habitats," and that he would use the summit of G7 leaders this weekend to call for a renewed focus on protecting nature.

Several hundred environmental activists also demonstrated outside the Brazilian embassy in Paris on Friday.

On Thursday, Bolsonaro told foreign powers not to interfere.