Story highlights FBI seeks public's help in identifying English-speaking militant

The ISIS fighter, possibly an American, appears to help execute Syrians in a video

The 55-minute video released by ISIS shows the jihadist leading a mass execution

In the video, jihadist speaks first in Arabic, then in English

The FBI on Tuesday asked for the public's help in identifying an English-speaking militant who appeared to help execute Syrian soldiers in an ISIS recruitment video released last month.

In the 55-minute video titled "Flames of War," the jihadist switches from classical Arabic to perfect English with a North American accent, and appears to orchestrate a mass execution of Syrian soldiers

The FBI reached out to the public on its website Tuesday, posting a portion of the video and asking whether anyone has information about the jihadist's identity.

"We're hoping that someone might recognize this individual and provide us with key pieces of information," Michael Steinbach, assistant director of the FBI's counterterrorism division, said Tuesday.

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The request is part of the FBI's broader outreach to the public to help identify people seeking to travel overseas to fight with terror groups, and those who are returning from such fights.

U.S. intelligence officials have been trying to analyze the recruitment featuring the English-speaking jihadist.

Officials see the killer's appearance in the video as significant because he comes across, they say, as articulate and persuasive, a person of influence within the terror group.

In the video, there are a number of men digging a ditch behind him. The jihadist, whose face is covered except for his eyes, claims they are Syrian soldiers assigned to a 17th Division military base near the Syrian city of Raqqa, and who, after an ISIS attack, were "digging their own graves in the very place where they were stationed."

CNN cannot independently verify that the men in the video were soldiers, as the propaganda video claims.

The video then shows the speaker and a group of militants executing the men, who fall into the ditch.

The man who led this atrocity on film could be an Arab who was educated in the West. Or he could be an American or Canadian. If so, CNN terrorism analyst Paul Cruickshank said, he would be the first North American jihadist to commit a war crime on camera.

"Clearly ISIS had a calculated step to be able to put this guy on camera," said Frank Cilluffo, a security analyst at George Washington University. "Why? Because he seems American. The message is aimed at a Western audience."

On Sunday, FBI Director James Comey told CBS' "60 Minutes" that his agency is tracking a dozen Americans that have joined terrorist groups inside Syria.

"These homegrown violent extremists are troubled souls who are seeking meaning in some misguided way, and so they come across the propaganda, and they become radicalized on their own, sort of independent study, and they're also able to equip themselves with training, again, through the Internet," Comey told CBS. "And then engage in jihad after emerging from their basement."

Last month, federal authorities detailed their case against the owner of a New York food store who they accused of funding ISIS and plotting to gun down U.S. troops who had served in Iraq.

A law enforcement official told CNN that former Boston resident and U.S. citizen Ahmad Abousamra could be a key player in the ISIS social media machine that's become renowned in recent weeks for spewing brutal propaganda online -- messages meant both to terrify and recruit Westerners.

And CNN obtained tapes of American terrorists recruiting friends in the United States to join terror groups like ISIS.

ISIS has successfully recruited large numbers of foreign fighters from across the globe, including from the United States and Western Europe.

A CIA source told CNN last month that more than 15,000 foreign fighters, including 2,000 Westerners, had gone to the civil war in Syria. It was not immediately clear how many had joined ISIS and how many were with other groups opposed to the Syrian government.

The foreign fighters come from more than 80 countries, the CIA source said.

A top State Department official insisted Monday that American efforts to combat ISIS' powerful online message are working , successfully keeping disaffected youth from joining the extremist group.

"We have evidence that there are young people who are not joining because we have somehow interceded," Under Secretary of State for Public Diplomacy and Public Affairs Richard Stengel told CNN's Elise Labott on Monday.

"They're reading the messages, they're hearing the messages -- not just from us but from the hundreds of Islamic clerics who have said that this is a perversion of Islam, from the hundreds of Islamic scholars who have said the same thing."

"It's a very small cohort," Stengel said of these so-called "foreign fighter" cases originating from the United States.