Brazil, Aug. 28 -- Acrimony between Brazil and European countries seeking to help fight Amazon fires deepened on Tuesday, jeopardizing hopes of global unity over how to protect a region seen as vital to the health of the planet.

A personal spat between the leaders of Brazil and France seemed to dominate the dispute, but it also centered on Brazilian perceptions of alleged interference by Europe on matters of sovereignty, economic development and the rights of indigenous people. Brazil said it will set conditions for accepting any aid from the Group of Seven nations, which offered tens of millions of dollars for firefighting and rainforest protections.

The Amazon's rainforests are a major absorber of carbon dioxide, considered a critical...