BONN - US President Donald Trump's threats to pull America out of the climate-rescue Paris Agreement is expected to cast a long shadow over UN talks starting Monday to work on the nuts and bolts of the deal.

The 11-day haggle in Bonn is meant to start drafting a "rulebook" to guide member countries in the practical execution of the pact, which seeks to brake global warming by curbing fossil fuel emissions.

But the negotiations risk being sidetracked by fears that the world's number two carbon polluter will withdraw and throw the entire process into disarray.

"Obviously, the speculation coming out of Washington is now at the top of our minds," environment and energy minister Thoriq Ibrahim of the Maldives told AFP.

This is the first round of negotiations under the UN's climate convention (UNFCCC) since Trump's ascent to the White House.

His predecessor Barack Obama, alongside China's Xi Jinping, led a diplomatic push which saw 195 countries seal the climate deal in the French capital in 2015, after years of tough bartering.

Widely hailed as the last chance to stave off worst-case-scenario global warming, the pact was savaged by Trump during his presidential campaign.

He called climate change a "hoax" perpetrated by China, and promised to "cancel" the deal as president.

With the rest of the world on tenterhooks ever since, Trump has said he will make his decision before the next G7 meeting on May 26-27 in Sicily.

"The question of whether this creates a difficult backdrop for the negotiations is clearly a 'yes'," said Paula Caballero, who heads the climate programme at the Washington-based World Resources Institute (WRI).

Some fear a US withdrawal from the agreement would dampen enthusiasm among other signatories for ramping up national emissions-cutting targets.

   - It's about 'competitiveness' -

Current pledges place the world on track for average global warming of around three degrees Celsius over pre-Industrial Revolution levels -- far over the limit of two degrees Celsius (3.6 degrees Fahrenheit) targeted in the Paris deal.

A State Department official confirmed last week that a US delegation will travel to Bonn, though it will be a "much smaller" one than in recent years.

"We are focused on ensuring that decisions are not taken at these meetings that would prejudice our future policy, undermine the competitiveness of US businesses, or hamper our broader objective of advancing US economic growth and prosperity," said the official, when asked about the US negotiators' brief.

The Trump administration has already proposed slashing funds for the UN climate science panel, for the Green Climate Fund that helps poor countries combat global warming, and for the UNFCCC itself.

The forum's budget is a key item on the Bonn agenda.

There has been a chorus of appeals from US and foreign business leaders, politicians and non-governmental organisations (NGOs) for Washington not to abandon the agreement -- including from the prime minister of Fiji, which will preside over the next round of high-level talks in November.

"Don't let the whole team down by leaving when we have a clear game plan and have put so many scores on the board," Prime Minister Voreqe Bainimarama appealed last week.

The key mission of the May 8-18 meeting is to start drafting "rules" for putting the agreement into action: what information must countries include in their emissions updates, for example, and how must they report?

The rulebook must be finished by 2018, when the first global emissions-cutting stocktake is due to be held.

"In Bonn this week it's important that progressive forces come together to manage any fall-out resulting from any US retreat," said analyst Mohamed Adow of Christian Aid, which tracks climate impacts on poor countries.-AFP