President Joe Biden will discuss saving the Amazon rainforest with Brazilian President Luiz Inacio Lula da Silva on Friday, but despite their alliance on the climate crisis the leaders of the Americas' two biggest countries still differ sharply on Ukraine.

US officials say the climate crisis -- and Brazil's crucial role as the country containing most of the world's largest rainforest -- will be a "top priority" during Biden's Oval Office discussions with the leftist leader.

Lula, who previously led Brazil from 2003-10, took office again in January after defeating right-winger Jair Bolsonaro.

It's unclear whether Biden will commit US money to the Amazon Fund, a project started by Norway in 2008 to help finance the fight against deforestation.

That project was recently relaunched by Lula after being suspended under Bolsonaro.

However, "the two leaders are aligned on the need to take bold action," a senior US official said.

Biden and Lula will also find much common ground when they discuss threats to democracy.

Brazil remains tense after a pro-Bolsonaro mob attacked government buildings last month, with the violent scenes highly reminiscent of when Donald Trump's supporters stormed Congress in 2021 following his election defeat to Biden.

Coincidentally, Bolsonaro left Brazil shortly before his term ended and is currently staying in Florida, Trump's home state.

When it comes to Russia's nearly year-old war against Ukraine, however, the two leaders will likely hit something of a wall.

Biden has spearheaded an unprecedented Western effort to rally behind Ukraine, providing aid, weaponry, military training and diplomatic support as the country struggles to repel the Russian war machine.

But several major democratic countries -- notably India, South Africa and Brazil -- have largely remained on the sidelines, refusing to help Ukraine militarily and sending mixed messages politically.

Lula has pushed for peace talks in Ukraine, while the United States is emphasizing the need for Ukraine to defend itself, ultimately allowing it to negotiate from a position of strength.

The senior US official, who spoke on condition of anonymity, insisted there was no major discord and that "we respect and support" Lula's peace initiatives.

However, he said Biden would be emphasizing the "objective realities" of Russia's invasion, in violation of international law, and Ukraine's right to self-defense.

"I think that the two leaders are going to have a very candid conversation about really how to move forward in a way that leads toward an outcome that is consistent with the commitments made under the UN Charter," the official said.

- Brazilian climate leadership -

Bolsonaro was close to Trump, even modeling his political style on the Republican, so the return of veteran leftist Lula to power is a boost for Biden.

This is particularly true on the issue of climate change, which Biden has made one of his biggest priorities -- starting by putting the United States back into the Paris climate accord after Trump had exited the historic deal, which aims to slow global warming.

Asked if the White House is keen on contributing to the Amazon Fund, the senior US official would not give details but noted that Biden's climate negotiator John Kerry was due to visit Brazil shortly.

"So it is something we want to drive with ambition," he said.

Climate crisis action will "be a defining characteristic of the relationship between the United States and Brazil and one where Brazil, I think, has a lot to really show the world," the official said.