The airstrikes against militants from Islamic State took place, the Pentagon said, a day after President Barack Obama authorised the use of military force to protect refugees.
Two US Navy FA/18 jets dropped 500-pound laser-guided bombs on mobile artillery positions that had been used by the militants to attack Kurdish forces defending their regional capital Erbil, where US diplomatic personnel are based, Pentagon spokesman Admiral John Kirby said in a post on Twitter.
Obama said on Thursday that the airstrikes would be used to protect US personnel and Yezidis, a minority sect concentrated in northern Iraq, who have been targeted by militants.
Thousands of Yezidis were stranded on a mountain after being driven from their homes earlier this week. The president also said American military planes are dropping food and water for thousands of Yezidis.
The extremists "have called for the systematic destruction of the entire Yezidi people, which would constitute a genocide", Obama said in remarks from the White House. "The United States of America cannot turn a blind eye."
The escalation in US involvement in Iraq comes as the Islamic State, the extremist group that has conquered swathes of northern Iraq since June, extended its advance by seizing the Mosul Dam, the country’s largest.
The Sunni militants’ offensive - and their threats to kill religious minorities - has panicked tens of thousands of people and emptied towns that for centuries have been home to Yezidi and Christian communities.
Mindful of the public's aversion to another lengthy war, Obama acknowledged that the prospect of a new round of US military action would be a cause for concern among many Americans. He vowed anew not to put American combat troops back on the ground in Iraq and said there was no US military solution to the crisis.
"As commander in chief, I will not allow the United States to be dragged into fighting another war in Iraq," he said.
Even so, he outlined a rationale for airstrikes if the Islamic State militants advance on American troops in Erbil and the US consulate there in the Kurdish region of Iraq. The troops were sent to Iraq earlier this year as part of the White House response to the extremist group's swift movement across the border with Syria and into Iraq.
Obama addressed the American people only after receiving assurances that three US military cargo aircraft delivering food and water to the Iraqis had safely left the drop site.
The Pentagon said the airdrops delivered a total of 20,000 litres of fresh drinking water and 8,000 pre-packaged meals.
The president cast the mission to assist the Yezidis as part of the American mandate to assist around the world when the US has the unique capabilities to help avert a massacre.
In those cases, Obama said, "we can act carefully and responsibly to prevent a potential act of genocide".