Fresh airstrikes have reportedly hit more suspected fighters from the Islamic State militant movement in Syria.
Five strikes are reported near the Iraqi border and others near the Turkish border.
This as reports in Britain say parliament could be recalled as early as Friday to vote on a plan to join airstrikes also taking place in Iraq.
The US President has met representatives of the five Arab nations who have joined the coalition to fight the ISIL militants: Saudi Arabia, the United Arab Emirates, Jordan, Bahrain and Qatar.
“I just want to say thank you to all of you,” said Barack Obama. “This is obviously not the end of an effort, but is rather a beginning. But I am confident we have got a partnership that is represented here that will be able to be successful.”
Iran says it was told in advance by the US about the strikes in Syria and was assured that forces of the Syrian President would not be targeted. The US says it did not talk about specific timing or targets.
France is taking part in airstrikes in Iraq but has ruled out any action in Syria, while the Dutch government says it is also now considering contributing some fighter jets.