When John Kerry lauded Brazil’s “recommitment” to ending illegal deforestation, the US climate tsar was inundated with replies from sceptics who warned that the Jair Bolsonaro administration was not to be trusted.

Brazilian diplomats are battling that same scepticism days ahead of a climate summit hosted by Joe Biden, which American officials have painted as a pivotal moment for relations between the US president and the rightwing Bolsonaro government.

In Brasília, top foreign policy officials say the Brazilian government has embarked on a new approach to the environment, pointing to its commitment in a letter to Biden last week to eliminate illegal deforestation by 2030 as a signal the nation was ready to embrace a more “positive” role.

The message, however, has been greeted cautiously by the nation’s western interlocutors, who fear Bolsonaro — a mercurial former army captain who counts the Amazon rainforest’s illegal loggers and miners among his voter base — could change tack at any moment.

Their concern has been exacerbated by the more pugnacious approach of Ricardo Salles, Bolsonaro’s environment minister, who is pushing western nations to provide billions of dollars in financial aid to Brazil’s environmental efforts, even before the country begins to tamp down on surging levels of deforestation.

Labelled “blackmail” by some environmentalists, the approach has spurred friction with western countries, which Brazilians diplomats are seeking to ease ahead of the virtual two-day summit beginning on Thursday.

“There has been a change in the government’s position. There has been a political decision to be positive and ambitious on the 22nd of April,” said Paulino Franco de Carvalho Neto, an ambassador at Itamaraty, Brazil’s foreign ministry.

“We are ready to co-operate with other countries,” he said, adding that the new approach had been adopted recently and came from Bolsonaro.

Leonardo Cleaver de Athayde, Brazil’s lead climate negotiator, said the shift in Brazilian policy was evidenced by “Bolsonaro’s commitment to ending illegal deforestation by 2030, [which] is a new and very significant political development and should be acknowledged as such”.

Franco also pointed to progress in negotiating a “side letter” with the EU to propel the EU-Mercosur trade deal, which has been stalled over environmental concerns, as well as the appointment this month of a new Brazilian foreign minister, Carlos Alberto França, who highlighted climate issues in his first speech.

The destruction of the Amazon has emerged as a key sticking point in Brazil’s relations with western countries over the past two years.

Since the beginning of the Bolsonaro administration in 2019, deforestation in the world’s largest rainforest has risen to its highest level in more than a decade, sparking concerns about the impact on climate change.

Last year more than 11,000 sq km of rainforest was razed, an area seven times the size of London, although it was still below the historic peak Brazil reached in 2008.

“We know we need to make important adjustments. We have a good history on sustainable development. Now is time to come back to this track,” said a senior official at Itamaraty.

The rhetoric, however, has failed to impress environmentalists, who said the goal to eliminate illegal deforestation by 2030 was merely a rehash of a pledge made by the previous administration under Dilma Rousseff.

A group of US senators have also lobbied Biden to take a firm line in the talks with Bolsonaro.

“In recent weeks, the Bolsonaro administration has repeatedly expressed interest in working with the US on environmental issues. But, until now, it has demonstrated no serious interest in working with the multiple actors within Brazil who would play essential roles in any serious efforts to save the Amazon rainforest,” according to the letter signed by 15 senators, including Bernie Sanders, the independent from Vermont, and Elizabeth Warren, a Democrat from Massachusetts.

“Given [its] record of unmet climate commitments, it is our view that any US assistance to Brazil related to the Amazon should be conditioned on the Brazilian government making significant and sustained progress in two critical areas: reducing deforestation and ending impunity for environmental crimes.”

US diplomats said the environment was now their number one bilateral issue with Brazil, which officials at Itamaraty have also acknowledged. Many at the foreign office hope the appointment of França, a traditional career foreign service diplomat, as minister will help ease relations with Washington.

However, current and former diplomats say there are limits to what he can achieve.

“The new minister represents a return to professionalism in dealing with foreign affairs. But his challenge lies beyond the foreign office’s reach,” said Rubens Ricupero, a former environment minister.

“In order to build better relations with the Biden administration he depends on people he does not control: Salles in environment and Bolsonaro himself. If there are no real changes in policies in these areas the best the new minister can achieve is damage containment.”