Witnesses on the ground told the British-based Syrian Observatory for Human Rights they saw 10 armored vehicles, and other equipment, roll out from a US base in Rmeilan in Hassakeh province and head toward neighboring Iraq.
The threats have intensified in recent days as the USA begins the withdrawal process from Syria on President Donald Trump's orders.
Trump's shock announcement on December 19 that he was withdrawing all 2,000 American troops from the conflict-wracked Middle Eastern country has led to concern among allies, including Israel, and prompted the resignation of his then defense chief Jim Mattis.
Residents near border crossings that are typically used by United States forces going in and out of Syria from Iraq said they had seen no obvious or large-scale movement of USA ground forces on Friday.
Several weeks later, national security adviser John Bolton said the withdrawal will have a longer timeline, and will not be undertaken until Kurdish fighters are protected and ISIS is defeated in the war-torn country. However, Ankara asked for more time and for postponing the start of joint patrols in Idlib due to its inability to provide security guarantees. If not, the Trump administration would be accused of abandoning an ally to a grim fate.
Turkey already occupies and effectively runs local affairs in vast territories in northwestern Syria, including Afrin which came under an intense Turkish military campaign a year ago that resulted in thousands of deaths and displacement of some 160,000 locals as Erdogan promised to give the region back to the "rightful owners, Arabs".
The battle against die-hard jihadists in remote areas along the Iraqi-Syrian border and the hunt for IS supremo Abu Bakr al-Baghdadi, the world's most wanted man, could last indefinitely.
"Even when there was no such decision [by Trump], our President said we are going to enter the region east of the Euphrates", Turkey's Foreign Minister Mevlut Cavusoglu told privately-owned NTV.
Turkey considers America's Kurdish allies of the YPG militia - who were vital in the ground war against ISIS - a terrorist group.