The blast hit the downtown area of Manbij, close to an US-led coalition patrol where talk of an American withdrawal from the city had led to heightened tensions.
Reuters, in a report from Beirut citing a USA official, had earlier said that four us troops were killed and three others were wounded when a suicide bomber set off an explosive vest near a restaurant in a Manbij town market.
Still, Pence's press secretary insists he had been briefed on the Manbij attack and said their "hearts went out" to the fallen. Multiple videos of helicopters in the area were posted to social media in the wake of the blast being reported.
USA officials told The Post that initial reports suggested four Americans may have died.
The US military has confirmed servicemen have been killed while on routine patrol in northern Syria.
Manbij, where the attack happened, has been controlled by a Kurdish-led militia, which has fought alongside USA forces.
This frame grab from video provided by Hawar News shows a damaged restaurant where an explosion occurred, in Manbij, Syria, Wednesday, Jan. 16, 2019.
Britain-based war monitor, the Syrian Observatory for Human Rights, said 16 people, civilians and USA servicemen, were killed in the attack.
But he added that the United States would "stay in the region and we'll stay in the fight to ensure that ISIS does not rear its ugly head again".
A Pentagon spokeswoman said that only two us troops had previously been killed in action in Syria.
The security zones should serve as protection for the Syrian Kurds, who fear a Turkish invasion after Trump announced his decision to withdraw all 2,000 U.S. troops from Syria. Manbij, however, is controlled by Kurdish fighters, considered by Ankara to be terrorists. Trump at first said it would be immediate, then within 30 days, and it now appears to be on a slower timetable - although early steps of withdrawal have begun. The U.S. also worked to slowly remove the Kurds from the Manbij Military Council, a group put in place by the SDF, in order to ease Turkey's concerns.
The military said it was still gathering information.
Manbij has been held by US -backed fighters allied to the Kurdish YPG militia since they took it from Islamic State in 2016.
Graham was among the most forceful GOP critics of Trump when he declared victory against ISIS last month and announced the USA would withdraw troops.
Another important development to watch is the upcoming meeting on Syria between Turkish President Recep Tayyip Erdogan and Russian President Vladimir Putin scheduled for January 23 in Moscow.