The strikes in oil-rich Deir Ezzor province "targeted infrastructure facilities used by groups affiliated with Iran's Islamic Revolutionary Guard Corps," Central Command (Centcom) spokesman Colonel Joe Buccino said in a statement.

Buccino said these "precision strikes are intended to defend and protect US forces from attacks like the ones on August 15 against US personnel by Iran-backed groups," when a number of drones targeted an outpost of US-led anti-jihadist forces without causing any casualties.

Tuesday's air strikes hit nine bunkers in a complex used for ammunition storage and logistics, the colonel told CNN separately.

The US military had originally intended to hit 11 of 13 bunkers in the complex but called off strikes on two after groups of people were seen near them, he said, adding an initial assessment indicated no one had been killed.

US forces "took proportionate, deliberate action intended to limit the risk of escalation and minimize the risk of casualties," the colonel said in the Centcom statement.

Hundreds of American troops are deployed in Syria's northeast as part of a coalition focused on fighting remnants of the Islamic State group.

There was no immediate confirmation of the US strikes from Syrian state media.

The attack came the same day that Iranian state media said a Revolutionary Guard general "who was on a mission in Syria as a military adviser" had been killed Sunday.

The reports did not say how the general was killed, only describing him as a "defender of the sanctuary," a term used for those who work on behalf of Iran in Syria or Iraq.

Iran says it has deployed its forces in Syria at the invitation of Damascus and only as advisers.

The Islamic Revolutionary Guards Corps (IRGC) is the ideological arm of the Iranian military and is blacklisted as a terrorist group by the United States.