Al-Nusra Front, Al-Qaeda's Syrian franchise, said the strikes on Syria were "war against Islam", and threatened to attack the worldwide interests of participating nations.
Seven targets were hit in Syria, the Pentagon said, including at the border crossing into Turkey of the besieged Kurdish town of Ain al-Arab, also known as Kobane.
The Syrian Observatory for Human Rights monitoring group said IS rockets hit the town for the first time since the jihadist assault began on September 16, wounding 12 people.
Royal Air Force Tornado GR4 jets took off from Britain's RAF Akrotiri on Cyprus for Iraq but returned to base without dropping their laser-guided bombs.
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"On this occasion no targets were identified as requiring immediate air attack by our aircraft," said a defence ministry spokesman in London.
Belgium and Denmark have also approved plans to join France and the Netherlands in targeting IS in Iraq, allowing Washington to focus on the more complex operation against its Syria base.
Washington warned that the jihadists could not be defeated in Syria by air power alone, saying that up to 15,000 "moderate" rebels would need to be trained.
"These states have committed a horrible act that is going to put them on the list of jihadist targets throughout the world. This is not a war against Al-Nusra, but a war against Islam," Abu Firas al-Suri said.
Today was the second time US-led air strikes had been reported around Ain al-Arab since the IS advance began.
President Recep Tayyip Erdogan said Turkey could take a military role in the coalition, the Hurriyet daily reported.
He said the government would go to parliament with a motion on October 2, after which "all the necessary steps" would be taken.