The so-called Islamic State, the region's most powerful Sunni jihadist group, has driven thousands of members of the Yazidi minority from their homes and is besieging the refugees on an exposed mountain.
Last week, the United States launched an air campaign to break the siege of Mount Sinjar, bring humanitarian relief to the Yazidis and support Kurdish troops protecting their capital Arbil.
"US military forces continued to attack ISIL terrorists in Iraq today, successfully conducting an airstrike on an ISIL mortar position north of Sinjar," the US Central Command said in a statement.
"All aircraft exited the strike area safely."
Yesterday, the Pentagon said the US military had flown between 50 and 60 sorties per day in support of the operation but did not reveal how many launched strikes or dropped humanitarian aid.