In the letter sent, Donald Trump told Recep Tayyip Erdogan to not be a fool.

Turkish President Recep Tayyip Erdogan put US President Donald Trump's letter, asking him not to "be a tough guy" or a "fool" and warning him he will be viewed as a "devil" if he sends his forces into Syria, into the dustbin, reports said on Thursday.

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

In the October 9 letter sent after US troops were pulled out of Syria, Trump told Erdogan: "Don't be a tough guy. Don't be a fool!"

"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," Trump wrote in the letter.

However, the same day the letter was received, Turkey launched a cross-border offensive against Kurdish-led forces in northern Syria.

The US has been criticised for withdrawing its troops from the area, a step seen as a cue for Turkish military to cross the border.