The attack comes weeks after President Trump tweeted that the U.S. had "defeated ISIS in Syria."
U.S. service members were among those wounded by an explosion in the Syrian city of Manbij, a senior Kurdish security official told NBC News on Wednesday.
The official said members of the U.S.-led coalition, including Americans, were caught up in an blast that happened in a market in the center of the city. The official could not confirm the number of injured or dead.
Forces were on foot in the city, which is located near the border with Turkey, when they were approached by a man in civilian clothing with explosives hidden under his clothes, the official added.
The explosion occurred at 1 p.m. local time (6 a.m. ET).
The attack comes weeks after President Donald Trump announced that he was withdrawing all U.S. troops from Syria immediately.
On Dec. 19, he tweeted that the U.S. had "defeated ISIS in Syria," adding that was the "only reason" to have troops on the ground there.
"We have won against ISIS. We have beaten them and we have beaten them badly," he said in a video posted on his Twitter account.
Administration officials later said the drawdown will happen more slowly.
However, a U.S. military official last week said that the U.S.-led military coalition in Syria has begun the process of withdrawing troopsfrom the country.
Col. Sean Ryan, spokesman for the coalition fighting the Islamic State group, told the Associated Press that the U.S. started "the process of our deliberate withdrawal from Syria."
He declined to give a comment on specific timetables or movements.