Seven targets were hit in Syria, the Pentagon 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 Syrian Observatory for Human Rights monitoring group said IS rockets also hit the town for the first time since the militant assault began on September 16, wounding 12 people.
Other targets in Syria included IS vehicles and buildings near Al-Hasakeh, as well as an IS command and control facility near Minbej, US Central Command said.
Meanwhile, Royal Air Force Tornado GR4 combat jets armed with laser-guided bombs took off from Britain’s RAF Akrotiri base on Cyprus for missions over Iraq but returned after seven hours without having used their weapons.
Gen Dempsey says ‘ground component’ crucial to goal of defeating militants
“On this occasion no targets were identified as requiring immediate air attack by our aircraft,” a defence ministry spokesman in London said.
Belgium and Denmark have also approved plans to join France and the Netherlands in launching air raids against the militants in Iraq, allowing Washington to focus on the more complex operation in Syria, where IS group is based.
Washington warned that the militants could not be defeated in Syria by air power alone, saying that up to 15,000 “moderate” rebels would need to be trained.
Saturday was the second time US-led air strikes had been reported around Ain al-Arab since the IS advance began.
Senior Syrian Kurdish official Newaf Khalil said the latest strikes hit the IS-held town of Ali Shar, east of Ain al-Arab, and destroyed several IS tanks.
Saturday’s strikes came a day after hundreds of Kurdish fighters crossed from Turkey to reinforce Ain al-Arab’s Kurdish militia defenders.
Coalition aircraft also pounded the Euphrates valley city of Raqa, which the militants have made the headquarters of the “caliphate” they declared in June straddling swathes of Iraq and Syria.
“At least 31 explosions were heard in Raqa city and its surroundings,” said the Britain-based Observatory.
The US and Arab allies began air strikes against IS in northern and eastern Syria on Tuesday, more than a month after Washington launched its air campaign against the militants in Iraq.
Washington had been reluctant to intervene in Syria, but acted after the militants captured more territory and committed widespread atrocities, including beheading three Western hostages.
A US defence official said on Friday that the Syrian mission is now similar to US-led air raids against IS in Iraq, with “near continuous” combat sorties.
Washington is also planning to train and arm 5,000 Syrian rebels as part of the effort, although the top US military officer, General Martin Dempsey, said between 12,000 and 15,000 men would be required to recapture “lost territory” in Syria.
Gen Dempsey said defeating IS would take more than air strikes and that “a ground component” was an important aspect of the US-led campaign.