Don't be a tough guy, don't be a fool, Donald Trump warns Erdogan.

WASHINGTON -- President Trump sent Turkish leader Recep Tayyip Erdogan an ominous letter last week after their Oct. 6 call, after which Trump controversially announced that the U.S. would withdraw all troops from northeast Syria ahead of a Turkish military operation in the region. The Oct. 9 letter, obtained by Fox Business Network's Trish Regan on Wednesday after Trump referenced it during a press conference the same day, advised Erdogan not to be a "tough guy" or a "fool" when it comes to his country's fragile situation at the Syrian border. Erdogan on Oct. 9 launched a Turkish military offensive into Syria, claiming it wanted to "neutralize terror threats" and establish a "safe zone." Turkish forces last Wednesday carried out airstrikes and later announced ground troops had invaded north-eastern Syria.

Nearly all U.S. troops there have been removed and will be redeployed in the region in the coming weeks. The president has been criticized by some analysts and political observers who insist he gave Turkey the "green light" to invade Syria and fight the Kurds, U.S. allies in recent efforts to bring the Islamic State to heel. Trump has defended his actions to "bring our soldiers back home" and put a stop to the "crazy endless wars," saying the United States is "7,000 miles away." "I didn't give them a green light," Trump said Wednesday, "and if anybody saw the letter...