Two Syrian opposition figures say the Islamic State group and al-Qaida's branch met last week and agreed to stop fighting each other and work together against their opponents.

The deal could be a heavy blow to Washington's strategy against the Islamic State group, relying on arming moderate rebel factions to push back extremists in Syria.

A prominent Syrian opposition official and a rebel commander say delegates from the two groups met in secret on Nov. 2 in northern Syria and agreed to end months of fighting between them and cooperate on the ground. The two spoke on condition their names not be used for their own protection or because they were not authorized to release the information.

The accord stops short of a merger between the two.