Turkish President Recep Tayyip Erdogan put US President Donald Trump's letter "in the bin".
In the letter dated 9 October, and sent after US troops were pulled out of Syria, Trump told Erdogan: "Don't be a tough guy. Don't be a fool!"President Trump was urging Turkey not to launch a military offensive against Kurdish-led forces in northern Syria, but Erdogan ignored this request.
US Vice President Mike Pence is now in Ankara to push for a ceasefire.
The US has faced intense criticism for the withdrawal of troops, which critics say gave Turkey the green light to launch the military attack.
In recent years, the Kurdish-led Syrian Democratic Forces (SDF) alliance has been a critical ally to the US in the fight against the Islamic State (IS) group in Syria.
There are fears that the destabilisation of northern Syria could lead to a jihadist resurgence.
What did Trump's letter say?In his letter to President Erdogan, Trump wrote: "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.
"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."
In response, Turkish presidential sources told BBC Turkish: "President Erdogan received the letter, thoroughly rejected it and put it in the bin."