A US solider wore the insignia of a Kurdish women's unit on his sleeve as US forces withdrew from northeastern Syria over the weekend.

The gesture reflected the anger many military personnel and veterans feel over the US decision to withdraw and leave the Kurdish-led Syrian Democratic Forces to face a Turkish incursion.

It's unclear if soldiers are authorized to wear ths insignia of non-US forces; Operation Inherent Resolve, the US-led anti-ISIS operation, declined to comment on the matter.

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A US solider wore a patch associated with the women's forces of the Kurdish People's Protection Unit, or YPJ, as US forces withdrew from northeastern Syria on Sunday.

A photo of the soldier, captured by Agence France-Presse photojournalist Delil Souleiman, shows him atop a US military vehicle in Tal Tamr, Syria, on October 20.

A green patch on the left arm of his uniform features a red star in the middle, a design featured prominently on Kurdish flags and other symbols.

According to Souleiman, the patch is from the women's forces of the Kurdish People's Protection Unit, or the YPJ, one of the partner forces under the umbrella of the Syrian Democratic Forces, which fought alongside US forces against ISIS in Syria.

On October 6, President Donald Trump announced that US forces stationed in northeastern Syria would pull out, leaving the area open to an incursion by Turkish and Turkish-backed forces. What began as an initial withdrawal of a few dozen troops spiralled into the departure of nearly all US forces in the country amid a deteriorating security situation.

Read more: Trump's withdrawal from Kurdish region has opened the door to a new wave of war crimes

A number of military veterans and leaders have decried the withdrawal, saying it is a betrayal of the SDF, which lost thousands of fighters during the years-long battle to defeat ISIS in Syria.

One veteran of the fight against ISIS called the US withdrawal from Kurdish-controlled northeastern Syria "a total slap in the face." Wes Bryant, a retired airman and coauthor of "Hunting the Caliphate: America's War on ISIS," previously told Insider that the decision was "a betrayal, at least of people with whom we were fighting a common enemy," and "a strategic blunder."

As US forces withdrew from parts of northeastern Syria and headed into Iraq on Monday, Kurds there threw rotten fruit and cursed the approaching vehicles, The Wall Street Journal reported. Video reportedly from the Syrian town of Qamishli appears to show men throwing stones at departing US Army vehicles.

The US Army piloted a program in 2016 that allowed units in the Army, the National Guard, and the Army Reserve to trade Soldier Sleeve Insignia (SSI) patches with soldiers in other US units with which they were partnering in order to build relationships.

However, the program only applied to partner units in the US military, and it is unclear if US service members are authorized to wear the insignia of a non-US force on their uniform. Insider reached out to Operation Inherent Resolve, the US-led anti-ISIS operation, for more information about regulations on insignia. OIR declined to comment.