The United States has indications other countries are willing to launch air strikes against Islamic State militants in Syria, its UN ambassador said yesterday, predicting "we will not do the air strikes alone".

Washington is trying to build an international military, political and financial coalition to defeat the radical Sunni Muslim group that has seized swathes of Iraq and Syria and proclaimed a caliphate in the heart of the Middle East.

US Ambassador to the United Nations Samantha Power was asked on CBS' "Face the Nation" if Washington had any indication other countries were willing to launch air strikes in Syria.

"We do," Power said. "But we're going to leave it to other nations to announce for themselves what their specific commitments to the coalition are going to be."

Power highlighted US efforts to build a coalition against Islamic State on television news shows as world leaders gathered in New York for this week's UN General Assembly.

The United States has launched air strikes against Islamic State within Iraq and President Barack Obama on September 10 authorised air strikes in Syria aimed at denying Islamic State fighters safe havens in either country.

Power refused to identify any of the countries that might join any air strike, but told CBS, "we do indeed have the support along the lines that I've described".