U.S. military vehicles pulled out of Syria on Monday — and were pummeled with what appeared to be rocks and rotting food in the process.

As tanks flying the American flag rolled through Qamishli, near the Turkey-Syria border, frustrated Syrian Kurds were filmed hurling small items at the withdrawing vehicles. Some ventured onto the exit route, attempting to block the troops' departure by standing in the streets with their hands up.

For many Kurdish residents, the pullout of U.S. troops by President Donald Trump roused feelings of abandonment. Kurdish fighters were instrumental in destroying the ISIS caliphate in Syria; the pullout of U.S. military forces near the Turkey-Syria border essentially paved the way for Turkish President Recep Tyyip Erodgan to launch a military offensive to clear the area of Kurdish groups — including those who fought alongside the U.S. — that he labeled a national security threat to his country.

Trump said he ordered the U.S. pullout as part of his campaign promise to end what he called the country's participation in "endless wars."

But his decision sparked widespread concern in the United States and around the world that the pullout could also create a military and political power vacuum that could lead to the resurgence of ISIS.

Some service members said that Trump's Syria withdrawal betrayed an ally, while Kurdish forces described the U.S. departure as "a stab in the back."

"When American troops first arrived in North Syria, Kurds received them as heroes with flowers and ululation. Now terrified Kurds in Syria are throwing tomatoes and stones at departing American forces," tweeted journalist Jenan Moussa before linking to another short video clip in which a male voice shouts: "It's the biggest betrayal in history. We will never forget that."

"Stones and rotten fruit for the withdrawing US force. What a farce this has been," tweeted ABC Middle East correspondent Adam Harvey.

Defense Secretary Mark Esper said Monday that the Pentagon is discussing keeping a "residual force" of U.S. troops in some Syrian cities to deny access to oil fields to ISIS and other groups that "might want to seek that revenue to enable their own malign activities."

The Pentagon chief said the plan was still in the discussion phase and had not yet been presented to Trump, who has repeatedly said ISIS has been defeated.

Esper emphasized that the proposal to leave a small number of troops in eastern Syria was intended to give the president "maneuver room" and wasn't final. "There has been a discussion about possibly doing it," Esper said at a news conference in Afghanistan before heading to Saudi Arabia. "There has been no decision with regard to numbers or anything like that."

The Associated Press contributed to this report.