Noor Jamal, who uses the nom de guerre Mullah Toofan, has reportedly been declared acting leader of the militants after Mehsud was mortally wounded in an American missile strike last month and is believed to have died.
Details of Mullah Toofan first emerged last week when he was seen in mobile phone video footage flogging two men and a teenage boy in Pakistan’s tribal belt.
Villagers told one newspaper the commander “kills humans like one will kill chickens”.
Mullah Toofan, aged in his early forties, has served the Taliban as a commander in the Orakzai and Kurrum tribal agencies.
Rehman Malik, Pakistan’s interior minister, said this week he has “credible” information Mehsud died from his wounds after the missile strike. While Taliban spokesmen have disputed this, intelligence reports have suggested he may have died en route to a clinic in Karachi.
Mullah Toofan will assume the leadership of a group blamed for thousands of deaths including the assassination of the former prime minister Benazir Bhutto.
Mobile phone footage shows Mullah Toofan flogging a man accused of speaking out against the Taliban and another who had neglected his prayers. A teenage boy was beaten for not growing a beard.
In Afghanistan, Taliban fighters on Thursday clashed with US marines outside Marjah in Helmand province. The militant-held town is the focus of Operation Moshtarak, the imminent Nato-led assault to clear the area of up to 1,000 Taliban fighters and win the confidence of local people.
American, Afghan and British ground forces have spent two weeks manoevering toward the town and assassinating Taliban commanders ahead of an attack they said would use “overwhelming force”.
Marines said the Taliban fighters were apparently trying to draw them into a bigger fight before they were ready to launch the main attack with an aerial assault.
Insurgents repeatedly fired rockets and mortars at the American and Afghan units poised in foxholes around the town, 380 miles south-west of Kabul.
The Taliban has threatened to plant large numbers of homemade landmines in the town.
Brig Gen Larry Nicholson, commander of the US marines in southern Afghanistan, said: “This may be the largest improvised explosive device threat and largest minefield that Nato has ever faced.”