"Will devastate Turkey economically if they hit Kurds", he tweeted on Sunday.
In a tweet, Trump also warned the Kurdish forces not to "provoke Turkey".
The U.S. provided military training and supplied truckloads of weapons to the YPG, disregarding warnings from Ankara that the YPG is organically linked to the PKK, and partnering with one terrorist group to fight another was not acceptable.
Erdogan, who has welcomed the pullout plan, last week accused Trump's national security adviser, John Bolton, of a "grave mistake" in demanding that Ankara provide assurances on the safety of the Kurdish fighters before Washington withdraws its troops.
"Although we made a clear agreement with U.S. President Trump, different voices are emerging from different parts of the administration", Erdogan said as Bolton prepared to leave town after meeting other Turkish officials.
Bolton, who recently travelled to Israel to reassure the U.S. ally of the Trump-ordered withdrawal, said there was no stipulated time for the pullout of American forces in Syria, but insisted that it was not an "unlimited commitment".
A US defense official told Fox News on Friday that the USA -led military coalition in Syria started the process of removing troops from the region, but wouldn't confirm further details for security purposes.
Trump announced the news in a Twitter post dated January 6, two days after the US military said it had carried out a strike targeting al-Badawi in Yemen.
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Trump did not detail who would create, enforce or pay for the safe zone, or where it would be located.
Ibrahim Kalin, a spokesman for President Erdogan of Turkey, responded to Trump's and said Turkey considered the Kurdish fighters terrorists.
"Starting the long overdue pullout from Syria while hitting the little remaining ISIS territorial caliphate hard, and from many directions".
The Pentagon has suggested positioning Special Operations troops in nearby Iraq, where they could attack in Syria if needed.
He repeated Ankara's threat to launch an offensive to eradicate Syrian Kurdish fighters from Syria.
With the help of the USA -led coalition, the SDF-a group of militias led by the Kurdish YPG-has driven ISIS out of northern and eastern Syria over the past four years.
Maria Zakharova, a Russian Foreign Ministry spokeswoman, said it was important for Syrian Kurds and the Syrian government to start talking to each other in light of the United States withdrawal plans.
But, he added, "we also know that those are fighting alongside of us for all this time deserve to be protected as well".
"Stop the ENDLESS WARS!" he added. Erdogan has vowed to crush it in the wake of Trump's decision to pull U.S. troops out of the region.
Presidential spokesman also said there was no difference between Daesh, PKK, PYD and YPG and Ankara would continue to fight them all.