Earlier on Tuesday, Marotto, via Twitter, provided additional details about the clash that took place the previous day and ended with no US troop casualties.
"On June 28, US forces in Syria were attacked by multiple rockets, approx. 34 x 122mm rounds of indirect fire," Marotto said.
The US forces have the inherent right to self-defense and responded with counter-battery fire at the rocket launching positions, Marotto also said.
"One Hellfire [missile] from a UAV [unmanned aerial vehicle] resulted in one enemy wounded in action," he added.
The US Defense Department reported earlier that rocket fire had damaged two buildings at a US military base guarding an oil field in the eastern part of Syria. The United States maintains some 900 soldiers in the country despite opposition from the Syrian government to their presence.