Syria's opposition on Monday called for air strikes to be immediately launched against Islamist fighters who have captured villages in the north -- or risk "catastrophe."

"We must begin air strikes immediately in Syria," Syrian National Coalition president Hadi al-Bahra told a news conference at UN headquarters in New York.

"As we speak, hundreds of thousands of civilians in the Kobane region of northern Syria are trapped by a brutal siege by ISIS," said Bahra, referring to the Islamic State organization.

"Time is of the essence to avert catastrophe."

More than 130,000 terrified Syrians fled to Turkey over recent days in the face of an advance by the jihadists, who already control vast swaths of territory in Syria and Iraq.

The United States and France have carried out air strikes in Iraq, at the request of the Iraqi government, and Washington is prepared to launch air assaults in Syria.

French Foreign Minister Laurent Fabius reiterated that in Syria, Paris would limit its aid to supporting the moderate opposition.

Bahra said that Islamist fighters were "advancing in a very speedy way," sweeping through "300 villages" and had "created a huge humanitarian crisis."

"You cannot sit and wait. You have to act," said the president of the SNC, the main exiled opposition group seeking the overthrow of Syrian President Bashar al-Assad.

Bahra plans to hold talks this week on the sidelines of the UN General Assembly to drum up support for action in Syria.