Syria attack deepens anxiety about U.S. drawdown

Bombing is deadliest combat incident since U.S. forces arrived in 2015

The deaths of four Americans in a suicide attack in Syria this week has intensified the military’s concern that the Islamic State terrorist group may step up attacks on U.S. forces to score a propaganda victory as the Trump administration withdraws.

Military officials have begun an investigation into Wednesday’s assault in the northern city of Manbij, which killed two U.S. service members, a Pentagon civilian and an American contractor. Five Syrians also died when a bomber detonated explosives in a restaurant where the U.S. personnel were meeting with allies, local officials said.

Current and former officials from the military and other U.S. agencies voiced concern Thursday that militants could launch similar assaults as the Pentagon executes President Donald Trump’s order to depart in coming months. Military officials said they believe IS conducted the attack.

“We are certainly aware that as we constrict and destroy the last remnants of the caliphate that [IS] has moved toward an insurgency,” one official said. “As that insurgency develops, we’ll be a prime target for that as we withdraw. Everyone’s aware of that, and it’s part of our planning.” The official spoke on the condition of anonymity to provide insight about what remains a sensitive military operation.

Wednesday’s attack, the most deadly combat incident in Syria since U.S. forces arrived in 2015, came nearly a month after the president declared victory against IS and announced that the U.S. force of about 2,000 troops would make a swift exit. Speaking at the Pentagon on Thursday, Mr. Trump offered his condolences to the families of those killed in Manbij. “We will never forget their noble and immortal sacrifice,” he said.

Mr. Trump’s unexpected exit order upended plans for an ongoing Syria mission and sent military forces scrambling to draft a plan to end its mission quickly.

Analysts said IS, which has been driven from most of the vast area it controlled at its peak in 2014, appears to sense an opportunity.

U.S. warplanes continue to conduct airstrikes in support of Syrian Kurdish forces battling remaining militant forces in far eastern Syria, a fight that has taken longer than many officials expected. The group also retains the ability to conduct guerrilla attacks across Syria, aided by a network of sleeper cells.

Charles Lister, a senior fellow at the Middle East Institute, said IS had embraced a tactic it used in previous years, in which a portion of its fighting force put down their arms and returned at least temporarily to civilian life.

“This kind of almost silence was to be expected,” Mr. Lister said. “Now, [IS] does have an opportunity to prove it is still there and humiliate the U.S. as it withdraws. There will be more bombings like this to send a message that ‘Yes, America says it has defeated us, but we’re still around.’”

Kenneth Pollack, a scholar at the Brookings Institution, said the group has a “strategic motive” for showing its ability to strike the United States at this moment.

“If they can claim credit for having driven the U.S. out of Syria or having accelerated the U.S. departure, that could really help them with their recruiting and support,” he said.

That attack also raised troubling questions about whether the American military had developed a false sense of security in a conflict zone, where avoiding predictable routines like a regular lunch spot can be a matter of life and death.

Several current and former special operations personnel, as well as other American officials who had worked in the region, said Thursday that [IS] had exploited a vulnerability.

“[IS] saw a target of opportunity, but they should have had better force protection,” a special operations officer said, speaking on condition of anonymity because he was not authorized to speak to the news media.

The Pentagon declined on Thursday to identify the four Americans killed, but military officials said one service member was an Army soldier and the other a Navy sailor, both enlisted personnel. The civilian was a Defense Intelligence Agency employee, and the contractor was an interpreter. At least one of the four, the Navy sailor, was a woman, the officials said.

Three other service members were wounded, a military official said.

Allied aircraft bombed a mosque on Thursday that IS had used as a command center in Safafiyah, Syria, in the Middle Euphrates River Valley, the Pentagon said. It was unclear if the airstrike was in response to the attack in Manbij, scores of miles to the northwest, or a target of opportunity.