Deir al-Zour, an oil-rich province that borders Iraq, is largely under Islamic State control and has been the focus of American-led airstrikes and other military action.
Since early 2015, the jihadists have besieged the provincial capital, also called Deir al-Zour, where about 200,000 people live. The Islamic State, also known as ISIS or ISIL, controls roughly half of the city, while the rest is held by forces loyal to President Bashar al-Assad of Syria.
Captain Davis said the raid was by the so-called expeditionary targeting force, a group of commandos from the secretive Joint Special Operations Command who target Islamic State leaders and fighters in Iraq and Syria.
The group has intensified drone strikes and raids in Syria in recent months against the Islamic State’s external operations planners, who have inspired, supported and directed attacks in the West.
The Pentagon announced last month that a United States airstrike had killed three Islamic State operatives who were involved in mounting terrorist attacks in Europe, including the deadly assaults in Paris in November 2015.
In August, a strike by an armed Reaper drone killed Abu Muhammad al-Adnani, the Islamic State’s spokesman, in a sign of what Pentagon officials said was the progress that the military’s Special Operations forces and the Central Intelligence Agency have made in the conflict’s two years by using information from spies on the ground and sensors in the sky to strike at Islamic State leaders.
Until his death, Mr. Adnani led the Islamic State’s external operations branch, and he in turn relied on two lieutenants. Those men have been identified by other members of the group by their noms de guerre, Abu Souleymane and Abu Ahmad, and their real identities remain debated.
Beyond these figures, little is known about the hierarchy of the branch of the Islamic State responsible for projecting terrorism abroad. The Pentagon’s announcement last month added at least three more names to the mix.
Salah Gourmat and Sammy Djedou, two of the three operatives the Pentagon said were killed last month, were described as “close associates” of Mr. Adnani who helped him plan and carry out the attacks that occurred in Paris on Nov. 13, 2015, leaving 130 people dead.
Killed along with the two Islamic state operatives was Walid Hamman, described as “a suicide attack planner,” who was convicted in absentia in Belgium for a plot that was thwarted in 2015.
On Monday, military officials did not identify the midlevel Islamic State leader targeted in Sunday’s raid or explain why he was important enough to risk the lives of American commandos.
In similar operations, American officials have said that detailed personal information recovered from laptops, cellphones and other electronic devices and materials seized in the raids had helped attacks against important terrorist leaders.
After a Delta Force commando raid in May 2015 killed a top Islamic State leader at his home in eastern Syria, American intelligence agencies extracted valuable information about the Islamic State’s leadership structure, financial operations and security measures by analyzing materials seized during the raid.
New insights yielded by that trove — four to seven terabytes of data, according to one official — included how the organization’s leader, Abu Bakr al-Baghdadi, operates and tries to avoid being tracked by coalition forces.
That raid on the residence of the leader, Abu Sayyaf, described by American officials as the group’s top financial officer, was one of the earliest major breakthroughs for American intelligence agencies in understanding the elusive terrorist network’s operations in Syria and Iraq.
Abu Sayyaf’s wife, Umm Sayyaf, who was captured in the operation, has provided information to investigators, one senior American official said.
When asked if Sunday’s raid also probably scooped up valuable intelligence, Captain Davis said, “You can infer that.”