"Let someone else fight over this long blood-stained sand," Trump said in a televised announcement. "The job of our military is not to police the world. Other nations must step up and do their fair share."
Trump said that sanctions on Turkish steel imposed on October 14 will be lifted "unless something happens that we are not happy with."
He said the US-negotiated ceasefire between Turkey and Kurdish-led Syrian Democratic Forces (SDF) will be permanent, but added: "you will also define permanent in that part of the world as somewhat questionable."
The president used his speech from the White House to defend his pullout of US forces from Syria even though he faces rare bipartisan criticism for the action.
Critics accuse the president of abandoning the Kurds - who fought alongside the US against the Islamic State - setting the stage for a possible Islamic State resurgence and leaving Syria to Russia's influence.
General Mazloum Abdi, who heads the SDF praised Trump's efforts saying he "stopped the brutal Turkish attack and jihadist groups on our people," according to a statement tweeted by his force's press office.
"Trump promised to maintain partnership with SDF and long-term support at various spheres," Abdi added.
Trump's announcement came hours after Russian military police started patrols in northern Syria under a new deal with Turkey that took effect on Wednesday to push back Syrian Kurdish militias from the border.
Syrian Kurdish militias have 150 hours, starting from noon (0900 GMT) Wednesday, to vacate the border zone.
The agreement between Ankara and Moscow leaves Turkey - a NATO member - and Russia in control of territory once held by the Syrian Kurdish forces who were backed by the US.
Erdogan's long-stated aim has been to control all 444 kilometres of Turkey's frontier with Syria.
Turkey also plans to create a "safe zone" along the border in Syria to facilitate the return of refugees.
A main concern as developments in Syria unfold is the fate of thousands of Islamic State fighters held in Kurdish prisons, some of whom have already escaped.
During his speech Trump said the fighters are under "lock and key" and the ones that escaped from Kurdish prisons are "largely recaptured."
But earlier on Wednesday Trump's top Syria envoy, James Jeffery, said over 100 Islamic State prisons have escaped, adding, "we do not know where they are."
Speaking to reporters Erdogan said the Turkish forces are not meant to stay in Syria.
"Syria is the real owner of these (areas). We are not an occupation army," Erdogan told reporters, according to embargoed comments released to Turkish media after the clock started on the new deal.
However, the Turkish-Russian patrols "will take place without a time limitation ... and within the depth of 10 kilometres" Turkish Foreign Minister Mevlut Cavusoglu said.
The joint patrols will start in the city of Kobane and extend to the Iraqi border after the 150-hour deadline, he said.
Despite Trump's defence chief saying Tuesday that Turkey appear to have committed war crimes in Syria, Trump praised Erdogan on Wednesday and said the two leaders "may be meeting in the very near future."
Turkey's incursion into Syria will be discussed at a NATO defence ministers' meeting in Brussels on Thursday and Friday.
NATO Secretary General Jens Stoltenberg said it was too early to judge the impact of the Turkish-Russian deal.
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