US forces in eastern Syria took indirect fire on Saturday but initial reports did not indicate any casualties or damage, a US defence official told Reuters.
The incident was the latest in a series of attacks on US personnel in Iraq and Syria in recent days.
The official, speaking on the condition of anonymity, said the attack occurred in Conoco, Syria.
US diplomats and troops in Iraq and Syria were targeted in three rocket and drone attacks on Wednesday alone, including at least 14 rockets hitting an Iraqi air base hosting US forces, wounding two American service members.
While there have not been immediate claims of responsibility for the attacks, analysts believed they were part of a campaign by Iranian-backed militias.
Iraqi militia groups aligned with Iran vowed to retaliate after US strikes on the Iraqi-Syrian border killed four of their members last month.
Iran has denied supporting attacks on US forces in Iraq and Syria and condemned US air strikes on Iranian-backed groups.
The United States has been holding indirect talks with Iran aimed at bringing both nations back into compliance with the 2015 Iran nuclear deal, which was abandoned by the Trump administration. No date has been set for a next round of the talks, which adjourned on June 20.