The comments came before a meeting of EU environment ministers in Cyprus this week to review last November's UN climate summit, which ended with a watered-down pact that omitted EU demands over fossil fuels.

Monique Barbut, France's minister for ecological transition, had already expressed disappointment over the outcome and said the EU must be prepared to "assert its red lines" and reject similar proposals in future.

The EU must be "less naive" and "more assertive, more demanding, and more transactional if we want to have an impact in these negotiations", her office said ahead of the Cyprus meeting.

"We are in a tougher world where the European Union, when it comes to climate negotiations, is more isolated," a senior source from Barbut's office told reporters.

"States that had previously been somewhat hesitant to speak out are doing so much more freely since the American withdrawal" from the global fight against climate change, the source added.

US President Donald Trump has withdrawn the world's largest economy from the Paris Agreement on global warming and the bedrock UN climate treaty that underpins it.

His administration sent nobody to the last UN climate summit in Brazil, where the EU's call for the inclusion of "roadmap" away from fossil fuels was left out of the final deal.

The EU ended up accepting it instead of scuttling a deal altogether.

The EU is the largest payer of climate finance -- money to help developing countries transition to a low-carbon future -- and Barbut's office suggested the 27-nation bloc could use this in a more "political" manner.

The source also questioned if the EU should "continue to demonstrate climate and financial solidarity with countries" that have failed to meet their obligations under the Paris Agreement.

These include updating their national pledges for cutting emissions, the latest round of which were due last year.

But more than 60 countries -- some of them major climate finance recipients such as India, Egypt, and the Philippines -- have still not turned in their latest plans.

"We have tools like trade agreements", whose implementation can be conditional on compliance with the Paris Agreement, the minister's office added.