"I want us to open the chapter for new submarines ... that we look nuclear propulsion in the face while being perfectly respectful of all non-proliferation commitments," Macron said at the launch of a conventionally powered Franco-Brazilian submarine in Itaguai near Rio de Janeiro. "You want it, France will be at your side."

Macron was speaking during a ceremony to launch Brazil's third French-designed submarine, which will help secure the country's long coastline, dubbed the "Blue Amazon."

The construction of the submarines was outlined in a 2008 deal between Lula and then French president Nicolas Sarkozy, which also included the purchase of 50 Caracal helicopters.

Brazil is also planning to build its first nuclear-powered submarine, the Alvaro Alberto, which would make it the first country outside the five permanent members of the UN Security Council to do so.

The French naval defense manufacturer Naval Group is supporting the design and construction of the submarine, except for the nuclear boiler which is being designed by the Brazilians.

Brasilia has been trying to convince Paris to increase technology transfers to help it integrate the reactor into the submarine and sell it equipment linked to nuclear propulsion.

France has been reticent to transfer such technology due to the challenges of nuclear proliferation.

"There are discussions on the possibility of France cooperating with us, including on nuclear energy, nuclear fuel," according to the European head of Brazilian diplomacy, Maria Luisa Escorel de Moraes, who recognizes that it is a "strategic, sensitive, delicate matter."

However, the project has suffered significant delays, mainly due to budget constraints, and the nuclear sub is now expected to be launched between 2036 and 2037, according to the Brazilian navy.

Macron is on a whirlwind tour of Brazil, a major economic ally, which kicked off Tuesday with the launch of a plan to raise over a billion dollars in green investments to protect the Brazilian and Guyanese Amazon.

The visit, the first by a French president to Latin America's economic giant in over a decade, is also a move to reset ties which had deteriorated significantly under former president Jair Bolsonaro.