Insurgents in Iraq have denied a government claim that the head of al-Qaeda in Iraq has been killed in an "internal battle" between militants.
Masri is believed to have formed al-Qaeda's first cell in Baghdad
The Islamic State of Iraq group, which includes al-Qaeda in Iraq, said Abu Ayyub al-Masri was alive, in an online statement which cannot be verified.
Earlier, Interior Minister Jawad al-Bolani said he had "primary information" showing Masri was dead.
But the US military said it was unable to confirm the minister's claim.
"I hope it's true, we're checking, but we're going to be doubly sure before we can confirm anything," Lt Col Chris Garver told reporters.
Several previous reports of Masri's death had been unfounded, he added. The US government has a $5m bounty on his head.
Masri, also known as Abu Hamza al-Muhajir, is believed to have trained in Afghanistan and formed al-Qaeda's first cell in Baghdad.
He has led al-Qaeda in Iraq since June 2006, when Abu Musab al-Zarqawi was killed in a US air strike.
The group is blamed for or has claimed some of the bloodiest insurgent attacks in Iraq since the US-led invasion in 2003.
Al-Qaeda in Iraq formed the Islamic State in Iraq with a number of other Sunni militant groups in 2006. The larger group is led by Abu Abdullah Rashid al-Baghdadi.
Masri was appointed the umbrella organisation's "minister of war" in mid-April, reports say.
In a statement posted on a website frequently used by insurgent groups, the Islamic State dismissed reports that Masri had been killed on Monday in clashes between insurgent groups and tribesmen in the Taji area, north of Baghdad.
Masri became head of al-Qaeda in Iraq after Zarqawi was killed
"The Islamic State of Iraq denies the death of the minister of war, may God protect him," the statement read.
"The Islamic State of Iraq reassures the Ummah [Muslim nation] of the safety of Sheikh Abu Hamza al-Muhajir, may God protect him, and that he is still fighting the enemies of God."
The group said it had published the denial "to reassure the hearts of Muslims".
"We caution them that the enemy continues to play on the tune of dividing the ranks of the mujahideen in Iraq," it added.
A spokesman for the Iraqi government said interior ministry sources had seen Masri being killed, but cautioned that they had not been able to identify the body because it was not in government hands.