Brazilian President Jair Bolsonaro said on Friday the country could open a vast reserve in the Amazon rainforest to mining, a move that his predecessor attempted before backtracking due to an international outcry by environmentalists.

The National Reserve of Copper and Associates (Renca) occupies roughly 46 100 km², an area slightly larger than Denmark, that is thought to be rich in gold, copper, iron-ore and other minerals.

"Let's talk about Renca. Renca is ours," Bolsonaro said at a televised event in Amapá state, home to part of the reserve.

"Let's use the riches that God gave us for the wellbeing of our population," Bolsonaro said. "You won't get any trouble from the Environment Ministry, nor the Mines and Energy Ministry nor any other."

Mining has been off-limits in the Renca, located in the northern states of Pará and Amapá, since it was established in 1984 to protect against perceived threats from foreign miners.

The reserve was established by a presidential decree and therefore can be revoked by the president without congressional approval.

Bolsonaro's predecessor, Michel Temer, abolished the reserve in 2017, only to reinstate it the following month after global backlash from environmentalists who said it would lead to a spike in deforestation.

"Brazil already had the chance to express its views on the opening of Renca to development, and public opinion was not favorable," said Adriana Ramos, legal and policy adviser at the Brazilian nongovernmental organization Instituto Socioambiental (ISA), in a statement.

"But the government prefers to announce controversial and outdated initiatives instead of new ideas for sustainable development in the Amazon," she said.

The Amazon, about 60% of which lies in Brazil, is the world's largest tropical rainforest. It is a bulwark against global warming and is sometimes called the "lungs of the world" because of the vast amounts of carbon dioxide its trees absorb.