Saddam Hussein's nephew was killed in a battle against pro-government forces in Iraq, according to the Baath Party and ISIS supporters.
NBC News was not immediately able to independently confirm the reports. Iraq's government did not comment.
Ibrahim Sabawi Ibrahim al-Hassan was the son of the late dictator's half-brother, a feared intelligence chief who died from cancer in 2013.
ISIS supporters posted images purporting to show al-Hassan late Tuesday and claimed he had died fighting for the militant group against Iraqi forces and Iranian-backed Shiite militias near Baiji, which is home to a key oil installation.
A website linked to Iraq's outlawed Baath Party said that al-Hassan had "joined the convoy of martyrs" in that battle. The website — which posts official statements from the outlawed party — said al-Hassan was 32 years old.
Al-Hassan was captured in 2005 by Iraqi and coalition forces near Saddam's hometown of Tikrit. He escaped from a prison near Mosul the following year while serving sentences for illegal weapons possession and the manufacture of explosive devices used in terror attacks.
His father — Sabawi Ibrahim al-Hassan — was at one point No. 35 on U.S. authorities' list of the 55 Most Wanted Iraqis and the Six of Diamonds in the deck of "Most Wanted" playing cards. He was captured in 2005 and received several death sentences, but died in a Baghdad hospital two years ago.
ISIS leader Abu Bakr al-Baghdadi has reportedly made a push to recruit former officers from the Sunni Baathist army, capitalizing on feelings of marginalization and sectarian politics inflamed by Iraq's Shiite-led government.
In tweets claiming al-Hassan's death, ISIS supporters said the fighter had disavowed the Baath ideology and pledged allegiance to their group.
Analysts say there are a number of former Baathists now in the Sunni militants' ranks.
"The marginalization of Sunni Muslim coupled with the de-Baathification of the Iraqi army left a lot of people feeling very dissatisfied with the state of affairs," said Charlie Winter, a researcher who monitors jihadist activity online for the London-based Quilliam Foundation. "ISIS is not only selling itself as a utopian, apocalyptic movement but it is also selling itself as a vanguard of Sunni Muslims in the region."
Some Baathists who've joined ISIS might fully have disavowed Baathist ideology and embraced jihadism, while others might be "bandwagoning simply because its perceived to be the best way to bring about change," Winter added.
The Associated Press contributed to this report.