Gen. Zahir Azimi, a spokesman for the Defense Ministry, said Mullah Brother is believed to have died in a U.S. air strike in Helmand province, after Afghan forces called for air support, Voice of America reported.

Mullah Brother was a military commander when the Taliban government controlled most of Afghanistan. He is said to be a relative by marriage and confidante of the Taliban leader, Mullah Omar.

While the Taliban has lost a string of leaders, the group continues to hold its ground in Afghanistan. A U.S. commander, Maj. Gen. Robert Cone, warned Thursday against putting too much trust in military action.

"The military will have a significant impact on the overall solution, but in reality, most insurgencies are dealt with by a political solution in the end," Cone told reporters in Kabul.