The US military reported late Monday that 22 US service members were injured in a helicopter "mishap" in northeast Syria on Sunday without divulging the reason for the event or defining the severity of the injuries.
The Central Command of the United States Military said ten service members were transported to higher-level treatment institutions outside the region.
The Central Command, which controls US forces in the Middle East, said no enemy fire was recorded but that the situation was being investigated.
Officials at US Central Command did not immediately respond to requests for additional information.
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Around 900 US forces are stationed in Syria, most of whom are in the east, as part of a mission to combat the Islamic State's remnants. In recent years, Iran-backed militants have repeatedly attacked American troops there.
25 US personnel were injured in bombings and counter-strikes in Syria in March, which also killed one US contractor and injured another.
During the Obama administration's battle against the Islamic State, US forces initially moved into Syria, collaborating with a Kurdish-led organization known as the Syrian Democratic Forces.
While the Islamic State is a shadow of the organization that declared a caliphate over a third of Syria and Iraq in 2014, hundreds of fighters remain camped in desolate areas where neither the US-led coalition nor the Syrian army, with support from Russia and Iranian-backed militias, have complete control.
Thousands more Islamic State fighters are being held in detention camps secured by the Kurdish-led Syrian Democratic Forces, America's main ally in Syria.
According to US experts, the Islamic State has the potential to regenerate into a significant threat.
Threats from Iran-backed militias to US forces highlight Syria's complicated geopolitics. Syrian President Bashar al-Assad leans on support from Iran and Russia and views American troops as occupiers.
