US Army Col. Ryan Dillon told reporters at the Pentagon that the US forces came under attack by small arms fire and that the engagement had resulted in "no damage to equipment or casualties on our side."
He added that the coalition troops did not return fire but added: "We do reserve the right to defend ourselves."
A US defense official told CNN that the engagements took place near the town of Manbij in northern Syria.
US troops have been performing "overt patrols" in the area since March, often flying the American flag from armored vehicles, in a bid to deter forces in the region from attacking one another and undermining the fight against ISIS.
The US trains and advises the Manbij Military Council, a group of local Arab fighters that is allied to the Kurdish-led Syrian Democratic Forces. But Turkey and its local Syrian allies are strongly opposed to both US-backed groups which they see as linked to Kurdish separatists in Turkey.
The US boosted its patrols in the region following armed clashes between the various groups.
While Pentagon spokesman US Navy Capt. Jeff Davis declined to call the troops "peacekeepers" upon their initial deployment in March, he referred to them as "a visible reminder for anybody looking to start a fight."
Dillon said that the attacking forces were most likely aware that they were firing on US troops.
"These patrols are overt. Our forces are clearly marked and we have been operating in that area for some time," Dillon said, adding "It should not be news to anyone that we are doing this, operating in that particular area."
Asked who among the various groups operating in the area was behind the attacks, Dillon said the coalition was unable to identify the attackers.
"We do not know who is behind these attacks," Dillon told reporters via video teleconference from Baghdad.
The US stepped up its patrols in Northern Syria in April after Turkey bombed US-backed Kurdish YPG fighters, a key element of the SDF.
Turkey has threatened to push on Manbij in the past, and if Turkey or more likely Turkish backed rebels were found to be behind the attacks, it could cause another major diplomatic rift between Washington and Ankara.
Dillon said that the coalition would continue to support local forces in the area.
"We will continue to advise our partners and reassure them in that area," he said.