Osama bin Laden and his deputy Ayman al-Zawahiri "parted ways" six years ago after he "marginalised" the al Qaeda leader, the Wall Street Journal reported citing a a senior Pakistani intelligence official.
Al-Zawahiri, who helped bin Laden found al Qaeda in 1988 and led its operation in Afghanistan and Pakistan, had been sidelined bin Laden because he no longer had the funds to support al Qaeda operations and that his popularity in the network was slipping, it said.
"They had parted ways some six years ago," the Pakistani official was quoted as saying.
But the Journal cited US officials as saying they have not heard of a split between the two men.
"Parted ways? I don't think so," one US counterterrorism official was quoted as saying. "I have not seen anything like that" in intelligence reports.
Another US official was cited as saying there was strong evidence, however, to support the contention that bin Laden had money problems. "We do know funding has been an issue," the official said.
Zawahiri has long been viewed as al Qaeda's chief ideologue and operational commander, with bin Laden seen as the mastermind and inspiration of the organization with a much less active day-to-day role.
Zawahiri is believed to be operating from a base in the Pakistani tribal regions, where bin Laden also was presumed by many to be, the Journal said.
A rift could help explain why bin Laden moved to the compound in Abbottabad, Pakistan, where he was killed in a raid by US forces in the early hours of Monday, it said.
Zawahiri was an Egyptian doctor and head of a radical jihadist group when he joined with bin Laden to create al Qaeda. Pakistani officials cited by the Journal said Zawahiri was behind most of the al Qaeda attacks in Pakistan.
Zawahiri, 59, is viewed as bin Laden's accepted successor. The Journal said according to al Qaeda documents assembled by US researchers, leadership succession inside the terror group is clearly laid out. The group's deputy will assume control if the leader is captured or killed.
The oath of loyalty sworn by al Qaeda members is to the position of leader - not to an individual. That means Zawahiri, though viewed by US officials as less charismatic than bin Laden was, would enjoy fealty from al Qaeda members, it said citing experts.