US troops pulled out of the region ahead of a Turkish incursion after Ankara cleared the attack on Kurdish regions in a phone call between Turkish President Recep Tayyip Erdogan and his American counterpart, Presstv Reported.
US media said on Tuesday that American troops were frustrated at President Donald Trump for his betrayal of the Kurds.
"They did everything we asked them to do," said one US defense official speaking to media, adding, "This is really not good for us."
Many Americans are concerned that Trump’s policies and sudden U-turns in agreements will make the US lose its credibility.
"How do we expect anyone to partner with us now?" another US defense official asked.
Turkey launched its long-awaited incursion into Syria using the country’s military forces and the Turkish-backed militants of the so-called Free Syrian Army (FSA).
The offensive targeted Kurdish areas where US-backed militants from the People's Protection Units (YPG) guarded the border areas.
Turkey said the objective of “Operation Peace Spring” was to neutralize terror threats against Turkey and lead to the establishment of a safe zone for Syrian refugees.
The Trump administration, which has threatened to slap "big sanctions" on Turkey, says Turkish troops would have attacked the Kurds even if the US troops were still there.
US lawmakers, however, have harshly denounced Trump's betrayal of the Kurds as a strategic blunder that will further tarnish US credibility, greatly weakening the international community's trust of US pacts and policies.