But the Pentagon is still working to determine whether the strike killed the militant, Briton Mohammed Emwazi.
Pentagon press secretary Peter Cook said the strike took place around the Syrian city of Raqqa, the Islamic State's de facto capital.
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"We are assessing the results of tonight's operation and will provide additional information as and where appropriate," Cook said.
If confirmed, Emwazi's death would cap more than a year of Western efforts to hunt down a militant who became widely known in August 2014 when he appeared - masked and dressed from head to toe in black - in a video in which he killed American journalist James Foley.
Emwazi subsequently appeared in grisly videos showing the killing of foreign hostages - speaking to the camera in taunting tones, with a balaclava over his face, a knife in his hand and a holster under his left arm.
Emwazi is thought to have participated in the executions of Steven Sotloff, another American journalist; Abdul-Rahman Kassig, an American aid worker; David Haines and Alan Henning, both British aid workers; and Japanese journalist Kenji Goto.
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Former Islamic State hostages have described Emwazi, one of a number of English-speaking captors dubbed "the Beatles" because of their British accents, as a vicious captor who waterboarded and beat hostages.
Officials, who spoke on the condition of anonymity to discuss a sensitive operation, said Thursday's strike targeted a vehicle and may also have hit another member of the group called the Beatles.
The Washington Post identified Emwazi early this year, but the identities of the other British militants have not become public.
The Britons are also thought to have held Kayla Mueller, an American hostage whose death was confirmed in February. Militants alleged that she was killed in a Jordanian airstrike, but U.S. officials have suggested she was killed by the Islamic State.
For more than a year, Western officials have sought to determine the whereabouts of Emwazi, who is thought to have made his way to Syria around 2012 and later joined the Islamic State.
Now in his mid-20s, Emwazi was born in Kuwait but grew up in a London family and studied computer programming before becoming radicalized. Emwazi was described by those who knew him before his militant days as a polite, fashionable young man who adhered to his Islamic faith.
Friends say his path toward militancy appears to have begun after his graduation from the University of Westminster, when he and several friends planned a trip to Africa, ostensibly to go to Tanzania for a safari. He was detained by authorities after arriving there and deported to Amsterdam, where he claimed to have been questioned by MI5, Britain's domestic security agency, and accused of having tried to travel to Somalia.
Somalia is home to another militant group, al-Shabab. Emwazi denied seeking to join al-Shabab.
Emwazi later moved to his native Kuwait, where he worked for a computer company, but he returned to Britain several times. In 2010, he was detained by British authorities and barred from leaving the United Kingdom. It is not known how or when he reached Syria.
Emwazi and the other so-called Beatles appeared to grow in stature and influence within the Islamic State over time. The group has used the detention and killing of foreign hostages, which has drawn intense attention in the West, as a tool for highlighting its power and goals.
Since it launched airstrikes over Iraq and Syria last year, the United States has killed a number of militants it has described as senior members of the Islamic State. But if Emwazi's death is confirmed, he would be by far the best-known militant to have been slain. The group's leader, Abu Bakr al-Baghdadi, remains at large.
Despite more than a year of U.S. and allied efforts against the Islamic State, the group remains a potent force that controls a wide swath of territory across Iraq and Syria.
In an attempt to accelerate the isolated successes that have occurred in recent months, the Obama administration late last month announced measures that will expand U.S. military involvement in both countries. For the first time, the Pentagon will position a small number of Special Operations troops on the ground in Syria.
