A picture taken on December 30, 2018, shows a line of US military vehicles in Syria's northern city of Manbij.

An attack in the northern Syrian town of Manbij has resulted in multiple casualties including U.S. troops, a senior Kurdish security official confirmed to NBC News.

The blast took place at 1:00 p.m. local time after a suicide bomber in civilian clothing approached coalition forces in the center of Manbij, according to the report. Four Americans, including two servicemembers, a Defense Department civilian and a DoD contractor, were killed.

ISIS claimed responsibility in a post via its Amaq news agency but did not produce evidence in support of the claim.

U.S. troops have been stationed in Manbij in support of local partners, the Syrian Democratic Forces, as part of the anti-IS coalition and as a buffer between Kurdish militias within the SDF and Turkish forces, who view the Kurdish fighters as terrorists.

The attack comes less than a month after President Donald Trump's surprise announcement to withdraw all U.S. troops from Syria, on the premise that ISIS had been defeated.

Despite a flood of criticism from lawmakers and security experts, the withdrawal process is now underway, according to the Pentagon, which has not disclosed details on a timeline or withdrawal numbers for "operational security" reasons.

The attack is likely to complicate the U.S. withdrawal, or potentially accelerate it, depending on the response of the American president.