Iraqi forces claim to have killed Izzat Ibrahim al-Douri, who served in Saddam Hussein's leadership circle and is believed to have been instrumental in the sudden rise of the self-declared Islamic State.
But an official from Saddam's Baath Party has denied the report.
Douri, 72, is the "king of clubs" in the deck of playing cards U.S. troops used to identify key figures in Saddam's regime following the 2003 invasion that toppled the Baathist regime.
Reuters says a spokesman for the Baath Party has denied the report in an interview with Al-Hadath television.
Saddam was executed in 2006, but Douri managed to elude capture and eventually came to lead the Naqshbandi Order insurgent group, which is believed to have helped spawn the Islamic State, or ISIS.
The BBC notes: "There have been reports of al-Douri's death or capture before, but correspondents say this is the most credible so far."
According to The Associated Press:
"Salahuddin province Gov. Raed al-Jabouri says soldiers and allied Shiite militiamen killed al-Douri early Friday in an operation east of the city of Tikrit. A graphic photo issued by the government purports to be of al-Douri's corpse.
"Senior regional commander, Gen. Haider al-Basri, told Iraqi state TV that al-Douri and nine bodyguards were killed by gunshots while riding in a convoy."
Reuters quotes Jabouri as saying the operation took place in the Hamrin Mountain area and that results of a DNA test from a sample taken from the body are "believed" to corroborate that it was Douri who was killed.
Last year, NPR's Leila Fadel reported that Douri had released an audio message in which he "urged unity for the fight for Baghdad and called fighters of the Islamic State and al-Qaida heroes."