United Nations Secretary-General Antonio Guterres said it is "absolutely essential" that the world implement the Paris Agreement, as US President Donald Trump faces pressure to keep the US in the climate deal.

CEOs of dozens of companies, including ExxonMobil Corp, Apple Inc, Dow Chemical Co, Unilever NV and Tesla Inc, urged Trump to remain in the agreement.

Tesla's Elon Musk threatened to quit White House advisory councils if the president pulls the US out, Reuters reported.

An anonymous source close to the matter told Reuters that Trump was preparing to leave the Paris accord. The source said Trump was working out terms of the planned withdrawal with US Environmental Protection Agency Administrator Scott Pruitt, an oil industry ally and climate change doubter.

Trump told reporters in the White House Oval Office: "You'll find out very soon." Earlier on Wednesday he tweeted that he will announce his decision "in the next few days".

"We believe that it will be important for the US not to leave the Paris Agreement," Guterres said in a Q&A section after his speech during an event at New York University on Tuesday. "But even if the US government decides to leave the Paris agreement, it's very important for the US society as a whole - the cities, the states, the companies, the businesses - to remain engaged with the Paris Agreement."

Guterres called for action to meet the climate challenge as he described the serious impact of climate change and opportunities presented by climate solutions to create jobs and build a foundation for a safer and sustainable world.

"The effects of climate change are dangerous and they are accelerating," he said. "It is absolutely essential that the world implements the Paris Agreement - and that we fulfill that duty with increased ambition."

"Climate change is undeniable, and climate action is unstoppable," he said.

The Paris Agreement, which took effect last November, aims to limit temperature increases caused mainly by greenhouse gas emissions. It was agreed to by the 195 member economies, including China and the US, under the Obama administration, which attended the 2015 United Nations Climate Change Conference in Paris.

China aims to cut its carbon emissions per unit of GDP by 60-65 percent by 2030 from 2005 levels and peak its carbon emissions by 2030, while the US aims to trim emissions by 26 to 28 percent from 2005 levels by 2025.

The secretary-general said that if any government doubts the global will and need for the accord, that is reason for all others to unite even more and stay the course.

"The message is simple: The sustainability train has left the station. Get on board or get left behind," he said. "Those who fail to bet on the green economy will be living in a gray future. Those who embrace green technologies will set the gold standard for economic leadership in the 21st century."

Guterres said that climate action is under way, and that countries and companies involved will reap the rewards.

"Thousands of private corporations, including major oil and gas companies, are taking their own action," he said. "They know that green business is good business. It is not just the right thing to do, it is the smart thing to do."

He said he intends to convene a climate summit in 2019 to reach the key first review of implementation of the accord.

Xie Zhenhua, China's special representative on climate change, said on May 22 in Berlin that China is preparing to address issues related to the implementation of the Paris Agreement.

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