US President Donald Trump sent a letter to his Turkish counterpart before Erdogan launched a raid on Syria, urging him to "Don't be tough" and "Don't be foolish!"
The October 9 letter, issued by the White House on Wednesday, came as Trump struggled to control criticism of his decision to withdraw US troops from northern Syria, paving the way for a Turkish military operation.
Turkey invaded northern Syria five days ago to fend off Kurdish-led forces from the border, accusing the Kurds of being terrorists.
The Kurdish forces in Syria are longstanding Western partners in the fight against the so-called Islamic State (IS).
"You don't want to be responsible for killing thousands of people," Trump wrote, "and I don't want to be responsible for destroying the Turkish economy – and I will."
He went on to warn Erdogan: "History will look upon you favorably if you do it right and humanly. It will regard you forever as the devil if good things do not happen."
"I'll call you later," Trump signed his letter.
The Turkish president said on Wednesday that Turkey's offensive in northern Syria will end only if the Kurdish-led forces withdraw.
It would be the fastest way to end the conflict, he said, adding that he was unwilling to negotiate his position.
The US House of Representatives voted overwhelmingly on Wednesday to condemn the withdrawal of President Donald Trump from US forces in northern Syria.
Democrats and Republicans have come together and passed a non-binding resolution declaring congressional opposition to the withdrawal of troops and saying Turkey should stop its military action in Syria.
The move said the White House should come up with a plan for an "enduring defeat" by IS.
. (tagsToTranslate) USA (t) Donald Trump (t) Recep Tayyip Erdogan (t) Turkey Syria Conflict