Washington (CNN) President Donald Trump is expected to withdraw from the Paris climate agreement , two senior US officials familiar with his plans told CNN Wednesday, a major break from international partners that would isolate the United States in global efforts to curb global warming.

The decision would put the US at odds with nearly every other nation on earth. It would reflect a major reversal of the Obama administration's efforts on climate change. And it could trigger further efforts to erode the landmark climate accord.

Trump will announce his decision in the White House Rose Garden at 3 p.m. Thursday, he tweeted . He ended his tweet with: "MAKE AMERICA GREAT AGAIN!"

I will be announcing my decision on Paris Accord, Thursday at 3:00 P.M. The White House Rose Garden. MAKE AMERICA GREAT AGAIN!

"I'm hearing from a lot of people both ways," he said as he met with Vietnam's prime minister in the Oval Office.

The precise mechanism for withdrawal hasn't yet been determined, and White House officials cautioned the plans could change until Trump makes his decision public. Language for the withdrawal was still being prepared Wednesday, and will likely include specific legal conditions crafted by Trump's administration.

In conversations over the past week, Trump has made clear he plans to fulfill his campaign promises to withdraw from the carbon reduction agreement, citing negative effects on jobs in the areas where he won a large percentage of the vote, including states in the Rust Belt and the western plains.

But Trump has changed his mind in the past on major issues, and was still speaking to opponents of withdrawal even as his team prepared an announcement. He is set to meet Wednesday afternoon with Secretary of State Rex Tillerson, who supports remaining in the agreement. On Tuesday, Trump met with a key voice advocating for withdrawal, Environmental Protection Agency administrator Scott Pruitt.

Speaking Wednesday, press secretary Sean Spicer said he wasn't sure whether Trump had made a final decision on withdrawing from the Paris agreement.

"I obviously don't know whether he's made it," Spicer said during an afternoon briefing. "When the President has a decision he will make that announcement and he will make it clear what the basis of that is."

I will be announcing my decision on the Paris Accord over the next few days. MAKE AMERICA GREAT AGAIN! — Donald J. Trump (@realDonaldTrump) May 31, 2017

The Paris climate agreement was established during a 2015 conference in the French capital. Every nation signed on minus two: war-torn Syria and Nicaragua, who insists the deal isn't tough enough. In signing onto the accord, countries pledged to reduce greenhouse gas emissions, but were given wide leeway in how much they planned to reduce them by.

The President's decision comes after months of internal debate and speculation about what Trump, who campaigned on leaving the deal, would do once he took office. Trump faced intense pressure on both sides, including from his senior advisers and family.

The White House was initially slated to make a final decision on the climate accord earlier this month, but delayed the decision until the G7 meeting in Sicily. At the summit, leaders expressed dismay at Trump's climate stance. After the meetings concluded, the US refused to sign onto a statement of support for the Paris accord that all other G7 participants approved.

German Chancellor Angela Merkel told reporters the climate conversations were unsatisfying. The leaders of the other G7 nations -- France, Japan, Canada, the United Kingdom and Italy -- all urged Trump to remain a part of the 2015 agreement.

Aides to Trump said he was listening with an open mind to the other leaders' arguments about Paris, but didn't feel obligated to heed their calls to remain within the pact. After he returned to Washington, Trump lashed out at Merkel over other matters, including NATO funding and Germany's trade deficit.

Trump's expected decision to withdraw was likely to raise further questions about US credibility abroad. Tillerson had argued to Trump in their discussions about Paris that scrapping the agreement could damage US negotiating power. Other major powers, including China, have signaled they will uphold their commitments to Paris regardless of Trump's moves.

"This would be a colossal mistake," said Nick Burns, who served as under secretary of state during George W. Bush's administration. "It would also devastate our international credibility. We are one of the two largest carbon emitters, with China. We are the ones who put this deal together. It is the first step to try to do something about climate change. For President Trump to take us out, it is anti-science."

Fierce divisions

Meetings inside the West Wing about Paris have been contentious , sources told CNN, as aides expressed their deep grievances over the climate agreement that President Barack Obama helped broker with nearly every country.

Steve Bannon, Trump's chief strategist and the former head of Breitbart, had pressed Trump to stick with his campaign promise and leave the deal.

But Ivanka Trump, the President's top aide and daughter, pressed aides to look at the full picture when considering what withdrawal could mean. She worked to ensure her father heard pro-Paris viewpoints, including from former Vice President Al Gore.

Trump's son-in-law and top aide, Jared Kushner, was said to be neutral on the deal, and concerned about the legal ramifications of reducing US carbon reduction commitments below what Obama pledged.

Tillerson and Energy Secretary Rick Perry had both advised against leaving the deal, sources said, joining a bombardment of voices from outside the White House. Elon Musk, the tech billionaire and founder of Tesla, tweeted earlier this month that he spoke with Trump about sticking with the deal. The president of Exxon Mobil wrote Trump personally stressing the importance of maintaining a seat at the global negotiating table.

Gore, who met with Trump during his presidential transition, has also been an outspoken critic of leaving the Paris accord.

But those voices were tempered by conservatives who argue the agreement harms American jobs and punishes US taxpayers. Trump himself said he would "cancel" the deal on the campaign trail and his campaign's energy plan included a pledge to "cancel the Paris climate agreement and stop all payments of US tax dollars to UN global warming programs."

A group of Republican US senators, including Majority Leader Mitch McConnell, wrote Trump earlier this month encouraging him to make a clean break from the climate accord. And leaders from coal-producing states have pressed Trump to uphold his vows to cancel US commitments to Paris.

Obama and a host of other countries signed the climate change agreement in 2015 and the former president touted it as the "best chance we have" to save the planet.

"The Paris agreement establishes the enduring framework the world needs to solve the climate crisis," Obama said, speaking from the White House. "It creates the mechanism, the architecture, for us to continually tackle this problem in an effective way."

The US committed to reducing carbon emissions by 26-28% in a decade in signing onto the agreement. The main driver of the reduction was Obama's Clean Power Plan, which would have closed coal-fired power plants. Trump has already said he's reviewing that order, along with other aspects of his predecessor's climate agenda.