U.S. officials have interrogated the fighters since they were first detained weeks ago, the official said.
The five were captured in the Manbij area by the Syrian Democratic Forces (SDF) several weeks ago, according to the U.S. official.
On Jan. 16, an ISIS suicide bomber exploded a bomb at a restaurant in Manbijg that was frequented by U.S. personnel stationed in the town.
The attack was the deadliest incident for American forces in Syria since they arrived in late 2015.
An SDF spokesman confirmed on Twitter that “a group of suspects” linked to the attack had been captured “following technical surveillance by our forces.”
The spokesman, Mustafa Bali, added that “the outcome of the ongoing investigation will be shared at a later time.”
Their capture was said to have been facilitated by the Manbij Military Council and other partners and the ISIS fighters have been under SDF detention since then.
Killed in the attack were Army Green Beret Chief Warrant Officer 2 Jonathan Farmer, Navy Chief Cryptologic Technician Shannon Kent, Ghadir Taher a contractor working as an interpreter, and Scott Wirtz, a civilian working for the Defense Intelligence Agency.
Three other Americans were injured in the blast.