Author and terror expert J.M. Berger, who has interacted with Hammami since he surfaced on Twitter this year and monitors Shabaab social networks, said that unlike past reports of his death, this time it seems likely to have happened.
"The evidence strongly points to this report being true compared to previous claims, which were weakly sourced. The sources in this case include people known to be close to Hammami," said Berger, a writer and analyst for IntelWire.
An African diplomat in the region told ABC News there is a "significant possibility" Hammami is dead, but final confirmation won't come without DNA tests.
A U.S. State Department official said the department is aware of the reports, but they are still "working to ascertain the facts."
A self-described representative for al-Shabaab have not immediately returned request for comment.
ABC News' Mike Levine contributed to this report.