Both Wali ur-Rehman, known as the chief military strategist, and Qari Hussain, chief instructor for suicide bombers, rank high on the Taliban hierarchy, The New York Times reports.
While Mehsud's death could set off a power struggle within the group, the report said it may be only a short one. A brief succession struggle came after Baitullah Mehsud, the previous leader, was killed last August in a similar drone attack.
Rumors about the death of the 28-year-old Hakimullah Mehsud began after Pakistan's state-run television reported he died of wounds suffered in the Jan. 14 drone attack and that he was buried recently. The Times quoted Pakistani and U.S. officials as saying Sunday they are increasingly convinced these reports are true.
Mehsud claimed responsibility for the Dec. 30 suicide attack at a U.S. base in Afghanistan in which seven employees of the Central Intelligence Agency died.
U.S. officials told the Times Mehsud's death would be a major blow to the Taliban as it fights escalating U.S. drone attacks and the Pakistani military's counterinsurgency.
But whether that would slow down the Taliban insurgency is not clear. After Baitullah's death, the violence increased with the Taliban targeting a number of Pakistani cities.
In a succession struggle, experts told the Times, al-Qaida may prefer Hussain, who trained with a sectarian group, Lashkar-e-Jangvi, over Rehman.