The US Central Command early on Tuesday said the attack was launched after Iraqi forces called for assistance - the first time the US had used force with the sole intention of directly supporting Iraq troops fighting the ISIL.
Previous US policy was to conduct air raids to protect US interests and personnel, assist Iraqi refugees and secure critical infrastructure.
Officials said the raid represented a broadened mission authorised by the US president, Barack Obama, to go on the offensive against the ISIL wherever it is.
They said another US air raid on Tuesday targeted ISIL positions near Mount Sinjar, an area in the north of the country where ISIL besieged the Yazidi religious minority, Al Jazeera reported.
In total, the strikes destroyed six ISIL vehicles near Sinjar and an ISIL fighting position southwest of Baghdad.
They bring the number of US air attacks in Iraq to 162 since US forces re-entered the country in August.
Earlier, a coalition of 30 countries, including western and Arab nations promised to combat the ISIL in Iraq and Syria, at a strategy conference in Paris. However, no coalition roles have been made public.