Washington has described Tuesday’s airstrikes against ISIL militants in Syria as “very successful”, adding that they’re only the beginning.
Activists said dozens of fighters from several groups were killed.
The White House says some of the strikes by US and Arab allies targeted a group linked to al Qaeda which had been plotting an imminent attack in the US or in Europe.
The Syrian government, which is also fighting ISIL, did not intervene.
Fifty targets were attacked in several parts of northern Syria.
In Raqqa one witness said the rockets had been precise and hundreds of militants had since vanished from the streets.
US President Obama has praised the Arab countries involved in the operation – Saudi Arabia, Qatar, Jordan, Bahrain and the United Arab Emirates – and says he is planning more talks to enlarge the alliance.
America, he says, is not fighting this campaign alone.
“We now have an opportunity to send a very clear message that the world is united, that all of us are committed to make sure that we degrade and ultimately destroy not only ISIL but also the kinds of extremist ideologists that lead to so much bloodshed.”
One resident of a town in Idlib province said civilian areas had been hit. The Pentagon said they’d struck only militant targets.
Some analysts in the US have questioned the effectiveness of the strikes in combating the Sunni Muslim extremists who have seized large swathes of Syria and Iraq, terrorising local populations.