U.S. President Donald Trump said Monday he was not "siding with anybody" on Syria after his decision to pull back troops. 

"I am not siding with anybody. We've been in Syria for many years. Syria was supposed to be a short-term hit. We were supposed to be in and out," Trump said during a press conference at the White House, adding he has "a good relationship" with his Turkish counterpart Recep Tayyip Erdogan. 

Trump has been facing mounting pressure in Washington after the White House announced late Sunday that the U.S. would pull back its forces in Syria ahead of a "long-planned" Turkish operation.

The Trump administration has ruled out any U.S. support for the operation, and in the face of significant pushback, the president vowed "if Turkey does anything that I, in my great and unmatched wisdom, consider to be off limits, I will totally destroy and obliterate the economy of Turkey."

In his remarks, the U.S. president said there were just 50 troops in the area where Ankara was planning to carry out the operation and did not want them to get hurt. 

"I think there is a lot of pressure on Turkey. They have been fighting with the PKK for many years," said Trump, adding the former Obama administration started the dispute and "natural war" between Turkey and the PKK, citing reports. 

A senior administration official speaking to reporters denied suggestions that Trump acted on the request of anyone, emphasizing the president's priority has been the protection of U.S. forces. 

The official further said the U.S. will not engage with Turkey militarily, noting Washington "is not in a position to, and will not be in a position to, fight Turkey over any actions that it takes with respect to Syria." 

"There's no green light. We're protecting our troops, and the president's made it very clear, that there should be no untoward actions with respect to the Kurds or anyone else," he said.   

Turkey has long called for the U.S. to partner with it in the fight against Daesh, a terrorist group Ankara has worked to root out, arresting and deporting its members within Turkey. 

Since 2016, Turkey’s Euphrates Shield and Olive Branch operations in northwestern Syria have liberated the region from YPG/PKK and Daesh terrorists, making it possible for nearly 400,000 Syrians who fled the violence to return home to western Syria.

In its more than 30-year terror campaign against Turkey, the PKK -- listed as a terrorist organization by Turkey, the U.S. and the European Union -- has been responsible for the deaths 40,000 people, including women, children and infants. The YPG is the Syrian branch of the PKK terrorist organization.