President Donald Trump wrote Turkish President Recep Tayyip Erdogan an unprofessional letter warning him not to be "a tough guy" or "a fool" while trying to bring forward negotiations to end the hostilities.
A letter obtained by Fox News correspondent Trish Regan, which was later confirmed by the New York Times as authentic, shows Trump taking an aggressive tone towards while trying to make a "good deal" with the Turkish President.
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Dated October 9, the letter reads: "Let's work out a good deal! 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. I've already given you a little sample with respect to Pastor Brunson.
"I have worked hard to solve some of your problems. Don't let the world down. You can make a great deal. General Mazloum is willing to negotiate with you, and he is willing to make concessions that they would never have made in the past. I am confidentially enclosing a copy of his letter to me, just received.
"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.
"Sincerely, Donald J. Trump."
According to Senate Minority Leader Chuck Schumer, Trump appeared to be proud of his letter as he handed out copies during a heated meeting with Congressional leaders, NBC News reports.
"The president is always tough at the wrong times. He should have been tough on the phone with Erdogan, not in a letter after he already green-lit Erdogan's invasion of Syria," Schumer said.
Republican-turned-independent Justin Amash of Michigan wrote that the letter was "insane" when he retweeted the post on Twitter.
Erdogan was apparently unswayed by the letter and has rejected calls to end military operations in northern Syria against Kurdish militias - that Turkey has long treated as a national security threat.
"Today, President Donald J. Trump spoke with President Recep Tayyip Erdogan of Turkey by telephone. Turkey will soon be moving forward with its long-planned operation into Northern Syria," the White House statement said. "The United States Armed Forces will not support or be involved in the operation, and United States forces, having defeated the ISIS territorial 'Caliphate,' will no longer be in the immediate area."
Over 100,000 people have been displaced so far in the chaotic battle between Kurdish militias and Turkish-led forces.