The Pentagon says two U.S. troops and two American civilians are among among those killed in a suicide bombing claimed by the Islamic State (IS) group in Syria.
"Two U.S. servicemembers, one Department of Defense (DoD) civilian, and one contractor supporting DoD were killed and three servicemembers were injured while conducting a local engagement in Manbij," the U.S. military's Central Command said in a statement.
A Syrian war-monitoring group said the blast near a patrol of the U.S.-led coalition in Manbij killed and wounded more than a dozen people.
The British-based Syrian Observatory for Human Rights said 16 people were killed, including at least five U.S.-backed Syrian fighters. It added that nine civilians and others were wounded in the blast.
The attack took place at a restaurant near Manbij's main market.
The U.S. troops were at the restaurant to meet members of the city's military council, a witness told Reuters.
U.S. Vice President Mike Pence said he and President Donald Trump condemned the attack, but reiterated that the United States would continue with its plan to withdraw troops from the country.
"Thanks to the courage of our armed forces, we have crushed the [IS] caliphate and devastated its capabilities. As we begin to bring our troops home ... we will never allow the remnants of [IS] to reestablish their evil and murderous caliphate," Pence said in a statement on January 16.
The attack came days after the United States began the process of withdrawing from Syria, pulling out equipment from the northeast into neighboring Iraq.
A news site affiliated with Islamic State earlier issued a statement saying an attacker with a suicide vest had targeted a patrol of the U.S.-led coalition operating in Manbij.
The Observatory's chief Rami Abdurahman said the blast was caused by a suicide bomber but didn't immediately offer any further details.