The US President Donald Trump warned Turkey's President Recep Tayyip Erdogan "don't be a tough guy" in a letter urging him to halt a military offensive in north-east Syria.
He told Mr Erdogan that he wanted to "work out a good deal" and that the Turkish leader was at risk of being viewed in history as "the devil".
In the letter, dated October 9th, Mr Trump wrote: "You don't want to be responsible for slaughtering thousands of people, and I don't want to be responsible for destroying the Turkish economy - and I will."
He added: "I have worked hard to solve some of your problems. Don't let the world down. You can make a great deal.
"History will look upon you favourably if you get this done the right and humane way.
"It will look upon you forever as the devil if good things don't happen.
"Don't be a tough guy. Don't be a fool! I will call you later."
A senior administration official has confirmed that the letter is authentic.
EXCLUSIVE: I have obtained a copy of @realDonaldTrump’s letter to #Erdogan. @POTUS warns him to not “be a tough guy! Don’t be a fool!” Says he could destroy Turkey’s economy if #Syria is not resolved in a humane way. Details tonight at 8pm #TrishRegan #FoxBusiness pic.twitter.com/9BoSGlbRyt
— Trish Regan (@trish_regan) October 16, 2019
Mr Trump is battling to control the political damage following his decision to pull US troops out of northern Syria, clearing the way for the Turkish incursion against the Kurds - America's former allies.
He has insisted the move was "strategically brilliant" after facing criticism for abandoning Kurdish fighters who helped the US defeat Islamic State militants in the region.
Senior Democrats Nancy Pelosi and Chuck Schumer walked out of a White House briefing on the situation on Wednesday, after accusing Mr Trump of throwing insults at them.
Ms Pelosi - who was allegedly called a "third-rate politician" by the president - claimed he appeared visibly "shaken up" after the House of Representatives passed a bipartisan condemnation of his decision to withdraw US troops from northern Syria.
She also posted a photo on her Twitter account, which showed her facing off against a visibly angry Mr Trump.
Image via @SpeakerPelosi on TwitterThe image was originally posted by President Trump with the caption: "Nervous Nancy's unhinged meltdown!"
But Ms Pelosi then used it as her Twitter wallpaper.
Speaking at the White House on Wednesday, Mr Trump said the Kurds were "not angels" and it might be necessary for Russian-backed Syria and Turkey to "fight it out".
"Our soldiers are not in harm's way - as they shouldn't be, as two countries fight over land that has nothing to do with us," the president said.
"Syria may have some help with Russia, and that's fine. It's a lot of sand.
"So you have Syria and you have Turkey. They're going to argue it out, maybe they're going to fight it out. But our men aren't going to get killed over it."
A US delegation - including Vice President Mike Pence and Secretary of State Mike Pompeo - are travelling to Turkey to speak to Mr Erdogan.
But the Turkish president has said he would not receive the US officials, and would only speak to Mr Trump. He later said he would meet the American delegation.
America's hasty exit from Syria has created a land rush between Turkey and Russia - now the undisputed foreign powers in the area - to partition the formerly US-protected Kurdish area.
Hundreds of IS prisoners have escaped during Turkey's military offensive.
