Turkey's President Recep Tayyip Erdogan threw away a letter from President Donald Trump in which he warned his counterpart of the consequences of military invasion in Syria, the BBC reported Thursday.

In the October 9 letter, Trump threatened to destroy the Turkish economy if Erdogan did not comply with US wishes and strike a deal with Kurdish forces in Syria.

He also told Erdogan not to be a "tough guy" or a "fool" in Syria.

Turkish presidential sources told the BBC on Thursday: "President Erdogan received the letter, thoroughly rejected it and put it in the bin."

Trump's letter departs from the conventional language of diplomatic correspondence, and has prompted widespread ridicule and criticism.

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Turkish President Recep Tayyip Erdogan threw a letter from US President Donald Trump warning him of the consequences of his military incursion into Syria "in the bin," the BBC reported on Thursday, citing unnamed Turkish government sources.

On Wednesday, a letter written by Trump to Erdogan on October 9 was leaked amid heightened criticism of Trump's decision to withdraw US troops from northern Syria, which effectively greenlit Turkey's military incursion into the region to fight Kurdish forces known as the YPG. The YPG and US were allies in the fight against ISIS in Syria.

"Don't be a tough guy. Don't be a fool!" the letter said. Its stark departure from the conventional language of international diplomacy left many to wonder whether it was genuine. The White House has confirmed the authenticity of the letter.

Trump also threatened to destroy the Turkish economy if Erdogan did not halt the invasion. "I don't want to be responsible for destroying the Turkish economy — and I will," he said.

Read more: 'It's utterly pathetic': Democratic lawmakers are flabbergasted by Trump's 'tough guy' letter to Turkey

On Thursday, Turkish presidential sources told the BBC that "President Erdogan received the letter, thoroughly rejected it and put it in the bin."

That same day, Turkish forces had launched an attack on the YPG in the region. The US withdrawal has led to dozens of ISIS prisoners escaping detention, and to the Kurds aligning with Syrian dictator Bashar al-Assad and Russian forces to defend against Turkey.

Trump's letter shows an attempt to push back against the Turkish invasion, despite his withdrawal being the act that triggered it. On Monday he also imposed sanctions on Turkish defense officials and steel imports in an effort to urge a ceasefire.

US Vice President Mike Pence is also scheduled to meet Erdogan on Thursday to urge an end to Turkish hostilities.

However, Erdogan has repeatedly refused to withdraw Turkish troops from Syria unti its objectives — destroying the Kurds — are met. Turkey considers the Kurds terrorists.

Turkish tanks and troops stationed near Syrian town of Manbj on October 15, 2019. Associated Press

Nonetheless, Trump has continued to defend his decision to withdraw US troops, claiming he was acting on a campaign promise to end US involvement in wars in the Middle East.

On Wednesday he also attacked the Kurds, claiming they were "no angels" and describing the Turkish PKK militant group as "worse than ISIS."

Read more: Trump is parroting Vladimir Putin's talking points as he defends pulling US troops from Syria