Afghan guerrilla commander Sirajuddin Haqqani, a possible successor to Taliban leader Mullah Akhtar Mansour, would likely prove an even more implacable foe of beleaguered Afghan government forces and their U.S. allies.

The United States killed Mansour in an airstrike in a remote border area just inside Pakistan, the Afghanistan government said Sunday, in an attack likely to dash any immediate prospect for peace talks. The U.S. has not confirmed Mansour's death.

Haqqani, who has a $5 million U.S. bounty on his head, is widely seen by U.S. and Afghan officials as the most dangerous warlord in the Taliban insurgency, responsible for the most bloody attacks, including one last month in Kabul in which 64 people were killed.