US government sources say the Pentagon and other national agencies are investigating the bombing This is one of the deadliest attacks on US forces in Syria since their deployment in 2015 WASHINGTON: The United States on Friday identified three Americans killed in a suicide attack in northern Syria this week that the US government said was likely carried out by Daesh Army Chief Warrant Officer Jonathan Farmer, 37, of Boynton Beach, Florida; Navy Chief Cryptologic Technician Shannon Kent, 35, identified as being from upstate New York, and Scott Wirtz, a civilian Department of Defense employee from St. Louis, died during the Wednesday attack in Manbij, Syria, the Department of Defense said. The Pentagon did not identify the fourth person killed, a contractor working for a private company. The Manbij attack on US forces in Syria appeared to be the deadliest since they deployed on the ground there in 2015. It took place in a town controlled by a militia allied with US.-backed Kurdish forces. Two US government sources told Reuters on Thursday that the United States views Daesh as likely responsible for the attack. The extremists claimed responsibility shortly after the attack. The attack occurred nearly a month after President Donald Trump confounded his own national security team with a surprise decision on Dec. 19 to withdraw all 2,000 US troops from Syria, declaring Daesh had been defeated there. If Daesh carried out the attack, that would undercut assertions, including by US Vice President Mike Pence several hours after the blast on Wednesday, that the militant group has been defeated. Experts do not believe Daesh has been beaten despite its having lost almost all of the territory it held in 2014 and 2015 after seizing parts of Syria and Iraq and declaring a "caliphate." While the group"s footprint has shrunk, experts say it is far from a spent force and can still conduct guerilla-style attacks. Trump’s Dec. 19 announcement was one of the reasons his former defense secretary, Jim Mattis, resigned. It stunned allies and raised fears of a long-threatened Turkish military offensive against US-backed Kurdish forces in northern Syria. How and when US forces leave has deepened uncertainty in northern Syria, with Turkey and Syrian President Bashar Assad ready to fill the vacuum. The US-backed YPG militia that is allied to the fighters holding Manbij last month invited Assad into the area around the town to forestall a potential Turkish assault. Syrian army troops entered the area soon after. The YPG-led Syrian Democratic Forces vowed on Thursday to ramp up attacks on Daesh remnants.