In this picture taken on Thursday, March 29, 2018, U.S. troop's humvee passes vehicles of fighters from the U.S-backed Syrian Manbij Military Council on a road leading to the tense front line with Turkish-backed fighters, at Halawanji village, north of Manbij town, Syria. The front line has grown more tense in recent days as Turkey threatens to advance on the town to clear it of the U.S-backed fighters. U.S troops have increased their patrols in the area, local commanders say, to prevent an outbreak of fighting and to prevent Turkey from advancing on Manbij. (AP Photo/Hussein Malla)
In this picture taken on Thursday, March 29, 2018, U.S. troop's humvee passes vehicles of fighters from the U.S-backed Syrian Manbij Military Council on a road leading to the tense front line with Turkish-backed fighters, at Halawanji village, north of Manbij town, Syria. The front line has grown more tense in recent days as Turkey threatens to advance on the town to clear it of the U.S-backed fighters. U.S troops have increased their patrols in the area, local commanders say, to prevent an outbreak of fighting and to prevent Turkey from advancing on Manbij. (AP Photo/Hussein Malla) Credit: Hussein Malla

A roadside bomb in northern Syria killed two coalition personnel, an American and a Briton, and wounded five others in a rare attack since the U.S.-led coalition sent troops into the war-torn country, the U.S. and British militaries and a U.S. defense official said Friday.

The military did not say where the attack took place or give the nationalities of the other casualties but it came hours after a local Syrian official said that a roadside bomb exploded in the tense, mixed Arab-Kurdish town of Manbij that is not far from the border with Turkey.

Manbij is under threat of a Turkish military operation. Ankara says Syrian Kurdish militiamen it views as “terrorists” and an extension of Kurdish insurgents inside Turkey are in control of the town.

The U.S. military statement said the attack happened Thursday night and that the wounded were being evacuated for further medical treatment. The statement said details were being withheld pending further investigation.

A Department of Defense official in Washington said one of the two killed was an American service member and the other was of another nationality.

No other information about the deceased American was immediately available. The official spoke on condition of anonymity because details had not yet been publicly released.

A U.K. defense ministry spokesman said the British armed forces member was killed during an operation against the Islamic State group. The spokesman added that an improvised explosive device killed the service member who was embedded with U.S. forces on Thursday.

No details on the casualty’s service branch, unit or gender were immediately provided.

The U.S. military member killed was the fourth American who has died in Syria since the U.S. began attacking Islamic State militants there in September 2014, according to the Pentagon’s Defense Casualty Analysis System.

Of the three previous deaths, Air Force Staff Sgt. Austin Bieren was specifically labeled by the Pentagon as a non-combat death. Another, Navy Senior Chief Petty Officer Scott C. Dayton, was killed by an improved explosive device. The third, Army Spc. Etienne J. Murphy, died in a vehicle rollover.

Earlier on Friday, U.S. military spokesman Col. Ryan Dillon couldn’t immediately say who was behind the attack.

“There is an investigation under way to identify who they could possibly be. We have our initial assessment and thoughts on that but we won’t provide until the investigation is complete,” he said.

Dillon declined to give the nationalities of the dead and wounded as well as the location of the attack until next of kin notification.

Dillon said the coalition has had fatalities in Syria before. “Perhaps by different means but there have been coalition deaths in Syria over the course of three years.”