The strikes hit seven targets in Syria, US Central Command said, including an IS building and two armed vehicles at the border crossing in the besieged Kurdish town of Ain al-Arab, also known as Kobane.
The jihadist advance on the town has sent 160,000 refugees streaming into Turkey.
Other targets in Syria included IS vehicles and buildings near Al-Hasakah, as well as an IS command and control facility near Minbej, near the western limit of the group's control, CentCom said.
The jihadists have made Raqa the headquarters of the "caliphate" they declared in June straddling swathes of Iraq and Syria.
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The strikes were carried out by US Air Force and Navy aircraft as well as by warplanes from Saudi Arabia, Jordan and the United Arab Emirates, the statement said.
In Iraq, three strikes were conducted southwest of Arbil, destroying four armed vehicles and a fighting position.
The US and Arab allies launched air strikes against the IS group in northern and eastern Syria on Tuesday, more than a month after Washington began its air war on the jihadists in Iraq.
A US defense official had told AFP yesterday that the Syria mission is now similar to US-led air raids against the IS group in Iraq, with "near continuous" combat sorties.