WASHINGTON — In a new online threat to American military personnel, the Islamic State has called on its members and sympathizers in the United States to kill 100 service members whose names, photos and purported addresses it posted on a website.

The group said that the personnel had participated in efforts to defeat it in Syria, Iraq, Yemen and elsewhere. 

Defense Department and F.B.I. officials said that they were aware of the website and were investigating the posting. 

It does not appear that the information had been hacked from government servers. One Defense Department official, who was not authorized to speak publicly, said that most of the information could be found in public records, residential address search sites and social media. 

The officials said the list appears to be drawn from personnel who have appeared in news articles about airstrikes on the militant group. Some of the names also appear to be drawn from the Defense Department’s own official reports on the campaign against the Islamic State, also known as ISIS and ISIL. 

But the list also included armed services personnel and others in the United States or elsewhere who have had nothing to do with the bombing campaigns, officials said. 

For instance, the list includes B-52 crew members stationed in Louisiana and North Dakota, but the air campaign is not using those bombers, the Defense Department official said. Several women are included on the list, but their faces in the photos were blurred. One of the photos appears to be at an official meeting with President Obama. 

American officials have grudgingly acknowledged the cleverness with which the Islamic State has used the Internet, in particular social media. The posting of military personnel includes names, photographs and other information neatly formatted. 

“With the huge amount of data we have from various different servers and databases, we have decided to leak 100 addresses so that our brothers in America can deal with you,” the Islamic State’s so-called Hacking Division said in the web posting. 

It added: “And now we have made it easy for you by giving you addresses, all you need to do is take the final step, so what are you waiting for?” 

The disclosure by the Islamic State highlights some of the challenges facing the military in balancing how it performs two essential functions: protecting its personnel while providing the American public with information. 

Unlike other parts of the United States government, in particular other agencies dealing with national security affairs, the American military allows members of the media to spend time embedded with its personnel in the field, granting permission to identify and quote them in reports. 

The New York Times