The letter “was not in line with diplomatic and political courtesy. We will not forget this lack of respect. This is not a priority for us. But when the time comes we would like it to be known that we will take the necessary steps.”
The extraordinary missive warned the Turkish leader not to be a “fool” over Turkish plans to start a military campaign in northern Syria.
“Don’t be a tough guy, don’t be a fool!”, the letter, leaked from the White House, said.
It emerged on Thursday that Mr Erdogan reacted angrily to the letter, throwing it in the bin and commencing the military offensive, which has left dozens of civilians dead and displaced hundreds of thousands.
In the 9 October letter, Mr Trump also told him he could make a “great deal” with General Mazloum Kobani, leader of the People’s Protection Units (YPG), the Kurdish-led militia that is allied with Washington in the fight against Isis.
He said he was offended by the suggestion that he would meet with Gen Mazloum Kobani. “You’re talking about a terror mastermind. This mastermind is talking to President Trump. This agreement is between Turkey and a state and not with a terrorist organisation.”
Turkey agreed on Thursday to a temporary ceasefire, but fighting has continued, according to Kurdish forces in northern Syria.
Speaking at a press conference in a chamber in the ornate Dolmabahce Palace complex along the Strait of Bosphorus in Istanbul, Mr Erdogan warned that the war could start again in earnest if the YPG does not vacate the 30 kilometre buffer zone along its border.
“If the US can keep its promise, the issue of safe zone will be resolved,” he said, referring to the YPG withdrawal. “If these promises are not kept at the end of 120 hour-period our operation is going to continue where it left off.”
US vice president Mike Pence and Secretary of State Mike Pompeo met with Mr Erdogan in Ankara on Thursday, after Mr Trump’s effective greenlighting of the offensive was met with widespread domestic and international condemnation.
The Turkish president called the meetings with US vice president Mike Pence and Secretary of State Mike Pompeo “very productive,” adding that “the next 120 hours we want to implement” the scheme.
Mr Erdogan said that he is heading to the Russian resort city of Sochi on Tuesday to meet with President Vladimir Putin and get him on board with his plan to create a 440-kilometre by 30-kilometre safe zone.