Iraqi officials are doing DNA tests on a militant killed during a US military raid to determine if he is al-Qaeda in Iraq leader Abu Hamza al-Muhajir.
Abu Hamza was identified in June as the late Zarqawi's successor
US military sources say it is probably not Muhajir, but they are awaiting confirmation from the tests.
An Arabic TV correspondent in Baghdad, quoting government sources, reported that Muhajir was killed in Haditha.
Muhajir took over as the al-Qaeda in Iraq leader in June after the death of his predecessor Abu Musab al-Zarqawi.
On Sunday, an Iraqi government official said the security forces were close to capturing Muhajir, also know as Abu Ayyub al-Masri, after showing the first video images recorded of him.
"There was a raid where we thought he may have been among those killed," said US military spokesman Lt Col Barry Johnson.
ABU HAMZA AL-MUHAJIR
Also known as Abu Ayyub al-Masri
Born in Egypt, trained in Afghanistan
Identified al-Qaeda in Iraq leader after death of Zarqawi
"We are still doing DNA tests but we do not believe coalition forces have killed al-Masri," he told Reuters news agency after initial reports of the death.
The raid took place two days ago, he said, but he refused to give further details.
An Iraqi government source, quoted by Reuters, said Muhajir and three of his comrades were killed in Haditha, in western Iraq, after US forces launched an air and ground assault on a safe house used by the al-Qaeda in Iraq group.
The group is believed to account for about 5% of anti-US insurgents in Iraq, but its suicide bombers have caused some of the worst bloodshed since the US invasion in 2003.
Little is known about Abu Hamza al-Muhajir. US military officials say he was born in Egypt and trained in Afghanistan, and he helped Zarqawi form the first al-Qaeda cell in Baghdad.