"Mansour has been an obstacle to peace and reconciliation between the Government of Afghanistan and the Taliban, prohibiting Taliban leaders from participating in peace talks with the Afghan Government that could lead to an end to the conflict," Cook said.
In the last year, the Afghan Government has been struggling to contain a resurgent Taliban, which has shown itself to be a still-powerful force as foreign troops have departed.
The US official said that the results of the strike were still being examined but that it appeared a second man travelling with Mansour, described as another combatant, was also believed to have been killed.