Syrian rebels said Friday they would retaliate for what they described as the assassination of one of their senior commanders by an al-Qaida-affiliated group, threatening to widen a rift between moderate and jihadist opposition forces fighting to topple President Bashar Assad.

The killing of Kamal Hamami, a member of the Western-backed Free Syrian Army's top executive body, comes amid heightened tensions on the opposition side as jihadist groups extend their influence in rebel-held areas of northern Syria.

Rebels said that Hamami, whose nom de guerre is Abu Bassir al-Ladkani, was shot dead Thursday in the coastal province of Latakia by gunmen from the Islamic State of Iraq and the Levant.