The strike, conducted on Tuesday, hit southwestern Libya, the U.S. Africa Command said in a statement, without giving the location. Residents of the city of Sebha said they heard an explosion to the south.
Two separate air strikes had killed 19 suspected militants in southern Libya, the U.S. military had previously said.
Some Islamic State militants retreated south into Libya’s desert as the group lost its stronghold in the coastal city of Sirte at the end of 2016.
The United States has said it will not allow militants to use a conflict between eastern and western-based factions around the capital Tripoli to protect themselves.
Eastern-based forces led by Khalifa Haftar launched an offensive to capture Tripoli in April, upending U.N.-led plans to broker a political settlement in Libya.