Donald Trump has been sending mixed signals about the Turkish operation in Syria, now in its second week: he first appeared to endorse it by withdrawing the 1,000 troops from the path of Turkish forces but a week later imposed economic sanctions on Turkey.

Turkish President Recep Tayyip Erdogan has discarded Donald Trump’s letter, in which he threatened him with potentially destructive economic sanctions, Turkish presidential sources told the BBC.

“President Erdogan received the letter, thoroughly rejected it and put it in the bin,” the sources were quoted as saying.

The letter was first obtained by Fox Business on Wednesday, after Trump referred to it during a press conference, and has been widely circulated online due to its unusual language: it is devoid of diplomatic niceties.

EXCLUSIVE: I have obtained a copy of ⁦@realDonaldTrump⁩’s letter to #Erdogan. ⁦@POTUS⁩ warns him to not “be a tough guy! Don’t be a fool!” Says he could destroy Turkey’s economy if #Syria is not resolved in a humane way. Details tonight at 8pm #TrishRegan #FoxBusiness pic.twitter.com/9BoSGlbRyt — Trish Regan (@trish_regan) October 16, 2019

“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,” Trump said in the letter.

He also told Erdogan, “Don't be a fool!” and “Don’t let the world down.”

The letter is dated Wednesday, 9 October, the day Turkey launched its cross-border military operation in northeast Syria. Just days prior to that, Trump and Erdogan had a phone call, after which the White House announced the pullback of US troops from positions in northeast Syria, effectively clearing the way for Turkish troops.

Writing in the Washington Post before the launch of the offensive, Erdogan’s communications director Fahrettin Altun said that Trump had “agreed to transfer the leadership of the counter-Islamic State campaign to Turkey”.

Ankara’s operation, code-named ‘Peace Spring’, targets formerly US-backed Kurdish fighters who gained control over the area during the eight-year civil war in Syria. Turkey believes those fighters to be terrorists tightly allied with the Kurdistan Workers’ Party, an outlawed group pushing for more Kurdish autonomy within Turkey.

The offensive, which aims to eliminate what Turkey considers to be a threat to its security, has been condemned by the Syrian government and a number of Western countries. Despite withdrawing the US troops – the only factor that had been stemming the Turkish army – Trump insisted that he did not endorse the operation, and imposed economic sanctions on Turkey this week.

President Erdogan said on Wednesday that he could “no longer” follow Trump’s shifting narrative on the operation.

Turkey’s president is meeting with US Vice President Mike Pence on Thursday for talks, which are expected to focus largely on the offensive.