The Pentagon said on Friday that two F/A-18 aircraft dropped 500-pound laser-guided bombs on a mobile IS artillery near the northern Iraqi town of Irbil.
Pentagon press secretary Rear Admiral John Kirby said in a statement that the Islamic militants had been using the artillery to shell Kurdish forces defending Irbil where US personnel are located.
"As the president made clear, the United States military will continue to take direct action against IS when they threaten our personnel and facilities," Kirby said.
President Obama on Thursday said the US had begun aid airdrops in Iraq's restive north, and would begin targeted airstrikes against militants from the "Islamic State" (IS) "if necessary."
It is not clear how many militants may have been hit or killed in the Friday strike.
Following the US strikes, Iraq's army chief of staff Lieutenant General Babaker Zebari said he now expected federal troops and Kurdish forces (called peshmerga) to reclaim large parts of land taken over by IS.
"There will be huge changes on the ground in the coming hours," Zebari told the news agency AFP.
shs/lw (Reuters, dpa, AP)