Brazil’s environmental authority has granted an initial permit to allow a major highway to be paved through the centre of the Amazon rainforest, the minister of infrastructure said, in a move that threatens to increase deforestation.

On the campaign trail, Brazil’s rightwing president, Jair Bolsonaro, had pledged to repave the road, called BR-319, that would connect the largest Amazon city of Manaus year-round to the rest of Brazil.

The road was originally constructed by Brazil’s military dictatorship in the 1970s but fell into disrepair in the harsh conditions of the rainforest. Much of the route is an impassable stretch of mud during the roughly six-month rainy season.

Paving the road would allow illegal loggers and land grabbers to more easily access remote and relatively untouched areas of the forest, environmental experts said. A study estimated the project would result in a fivefold rise in deforestation by 2030, the equivalent of an area larger than the US state of Florida.

Bolsonaro’s weakening of environmental protections has already spurred soaring deforestation, with clearing of the Brazilian Amazon hitting a 15-year high in 2021.

On Thursday, Marcelo Sampaio, the infrastructure minister, announced the permit on Twitter, posting an image of the licence from the environmental agency Ibama.

“In an alignment of engineering and respect for the environment, we are going to take the society of Amazonas state out of isolation,” he wrote. Sampaio did not immediately respond to a questions about environmental concerns.

The initial licence will allow the government to contract companies to pave the largest middle section of the road that is in worst condition. Contractors will draw up plans but would need another permit in order to begin construction.

This first licence would stipulate many conditions in the plans that must be met to start construction, said Marco Aurelio Lessa Villela, a former environmental analyst at Ibama.

“There must be an enormous list of things … that would be necessary for a road in that place not to be a tragedy,” Villela said.

An initial licence meant a good chance the road could move forward, he said.

Bolsonaro celebrated the licence in his weekly live internet address. “I hope soon there’s one more licence on the way and our [transportation department] can start bidding and work for paving BR-319.”