The raid - the most significant since the United States withdrew from Iraq - came a day after President Barack Obama authorized force as he voiced fears of genocide against minorities.
Two US F/A-18 aircraft dropped 500-pound (225-kilogram) laser-guided bombs on a mobile artillery piece near the Kurdish region's capital of Arbil, said Pentagon spokesman Rear Admiral John Kirby.
The United States bombed the position after Islamist fighters shelled Kurdish forces defending Arbil, where US personnel are stationed, he said.
The strike, carried out at 1045 GMT, targeted the Sunni Muslim extremist movement Islamic State of Iraq and the Levant that has swept across Syria and Iraq.
Obama, who opposed the 2003 invasion and has vowed no return of ground troops, said Thursday that he authorized action due to fears of genocide as thousands of members of the Yazidi minority fled for their lives.
On Thursday, the United States dropped thousands of gallons of drinking water and 8,000 packaged meals to Yazidis who risk starvation as they cram onto Mount Sinjar.
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