Syrian state media, citing a military source, said U.S.-led jets attacked a Syrian army position near the battle front against the last Islamic State pocket east of the Euphrates late on Saturday, causing damage and injuries.
A spokesman for the U.S.-led coalition, which is fighting a last Islamic State pocket east of the Euphrates, said its local allies had been fired on and "exercised their right to self defence", adding that the incident was under investigation.
"U.S. coalition aircraft launched an aggression this evening against one of the Syrian Arab army formations operating in the Albukamal area in the southeastern countryside of Deir al-Zor," state news agency SANA cited the source as saying early on Sunday.
The attack injured two soldiers and destroyed an artillery piece, the source added.
Coalition spokesman Col. Sean Ryan said in an email: "Our partner forces were fired upon and exercised their inherent right to self defense."
Islamic State now holds only a couple of villages in Syria, having lost almost all its territory in 2017 to two rival offensives, one by the U.S.-led coalition with local fighters, and one by the Syrian army and allied militia backed by Russia.
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The jihadist group also holds an enclave of desert surrounded by the Syrian army in the center of the country.
Its territory on the Euphrates was "down to the last two villages", Ryan said, adding that the coalition expected these to "clear soon", and that Islamic State's remaining fighters there were mostly foreigners.
Russia and the United States maintained military communications to prevent unplanned conflict between the two forces fighting Islamic State. However, some clashes have occurred.