A facility housing U.S. troops in eastern Syria came under attack late Sunday when rockets were fired from nearby areas, an opposition war monitor and a spokesman for U.S.-backed fighters said.
No one was hurt in the attack in which two rockets were fired at al-Omar field in Syria's eastern province of Deir el-Zour, according to Siyamend Ali, a spokesman for the U.S.-backed and Kurdish-led Syrian Democratic Forces. He added that it was not immediately clear where the rockets were fired from.
The Britain-based Syrian Observatory for Human Rights said the rockets were fired from areas controlled by Iran-backed fighters in the area of Mayadeen, also in Deir el-Zour.
The U.S. military did not immediately respond to a request for comment.
The rocket attack came six days after U.S. troops in eastern Syria came under a similar attack. Last week's attack came a day after U.S. Air Force planes carried out airstrikes near the Iraq-Syria border against what the Pentagon said were facilities used by Iran-backed militia groups to support drone strikes inside Iraq.
Hundreds of U.S. troops are stationed in northeastern Syria, working with the Kurdish-led Syrian Democratic Forces to fight against the Islamic State group.
Thousands of Iran-backed militiamen from around the Middle East are deployed in different parts of Syria, many of them in areas along the border with Iraq.
Iran-backed fighters have joined President Bashar Assad's forces in Syria's 10-year conflict. Their presence helped tip the balance of power in Assad's favor.