US Vice President Mike Pence is on his way to Turkey to urge President Recep Tayyip Erdogan to stop his offensive on Kurdish fighters in northeastern Syria.

The US has called for a ceasefire, but Erdogan has so far refused because he sees the Kurds as terrorists. The Kurdish forces were the US' allies in fighting ISIS in Syria.

But President Donald Trump undermined Pence's negotiating position on Wednesday, just as Pence was leaving, by saying that fighting in Syria is "between Turkey and Syria. It's not between Turkey and Syria and the United States."

Trump paved the way for the Turkish incursion earlier this month by abruptly withdrawing US troops from northeastern Syria.

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President Donald Trump undermined Vice President Mike Pence's mission to Turkey just as Pence was setting off, by publicly saying that the conflict is nothing to do with the US.

As of Thursday morning, Pence is en route to Turkey to meet President Recep Tayyip Erdogan to urge him to stop his offensive on Kurdish fighters in northeastern Syria, near the Turkish border.

They are scheduled to meet Thursday.

US Secretary of State Mike Pompeo, National Security Advisor Robert O'Brien, and envoy to Syria Jim Jeffrey are also part of the US delegation.

Turkey's President Recep Tayyip Erdogan in Belgrade, Serbia, on October 7, 2019. Associated Press

Trump tries to wash his hands of Syria

Turkey has long threatened to wipe out the Kurdish forces, which it sees as terrorists. Trump's October 6 withdrawal of US troops from northern Syria has paved the way for a Turkish incursion into the area, which is rapidly reshaping the territory.

The Kurds — with whom the US allied to fight ISIS in Syria — have since allied with Syrian dictator Bashar al-Assad and Russian troops to fight Turkey.

On Wednesday, Trump undercut Pence's bargaining power with Erdogan by saying that the US is not involved in the conflict.

Speaking to reporters at the White House, he said the conflict is "between Turkey and Syria. It's not between Turkey and Syria and the United States."

Of the remaining powers on the ground, Trump said: "They've got to work it out."

Read more: Trump is parroting Vladimir Putin's talking points as he defends pulling US troops from Syria

People standing on a rooftop in Akcakale, a Turkish city near the Syrian border, watch smoke billowing from fires caused by Turkish bombardment in Tal Abyad, Syria, on October 13, 2019. Lefteris Pitarakis / Associated Press

Jeffrey Prescott, an Obama-era senior national-security official, told the Associated Press that Trump's remarks hamper Pence's ability to "to have an impact on foreign policy."

He noted that Pence's stems from which "his ability to speak credibly for the president," which is diminished when they are public at odds.

"Given how erratic president Trump's decision-making process and style has been, it's just hard to imagine any country on the receiving end of another interlocutor really being confident that what Pence and Pompeo are delivering reflects Trump's thinking at the moment or what it will be in the future," Prescott said.

Read more: US troops and their allies feel humiliated after abandoning their bases in Syria to be taken over by gleeful Russians

Pence in the White House East Room on October 16, 2019. Leah Millis/Reuters

Earlier on Wednesday Trump defended his decision to pull out of northeastern Syria by saying that the Kurds were "no angels," and that they would survive because they "know how to fight." Around 11,000 Kurdish troops died fighting ISIS alongside the US.

The US withdrawal has also led to dozens of ISIS prisoners escaping from detention.

The Trump administration imposed sanctions on Turkey in an attempt to punish it over its Syrian invasion, and demanded a ceasefire.

Erdogan, however, has refused to call off his troops, telling his country's pro-government Daily Sabah newspaper that "we never will" declare a ceasefire.

"No ceasefire is possible in Syria until the People's Protection Units [Kurdish fighters] evacuates the border area. I told him [Trump] that Turkey will not negotiate with terrorists," he added.

An October 9 letter from Trump to Erdogan, leaked Wednesday, also shows Trump pressing for negotiations to end for hostilities by telling his counterpart not to be a "tough guy" or a fool." According to Middle East Eye correspondent Ragip Soylu, Erdogan "dumped Trump's letter to the trash."

Read more: Trump wrote a letter warning Erdogan not to be a 'tough guy' over Syria, telling him history will look upon him 'forever as the devil if good things don't happen'