Abou Zeid's death casts further uncertainty over the fate of the French hostages his group is still believed to hold.

In December, before the French intervention in Mali, he accused the French authorities of blocking negotiations for their safe release. Several of the hostages had appeared in videos warning against military intervention for the sake of their own safety. In one video, with masked men holding AK-47s behind them, the men look exhausted and terrified.

Andrew Lebovich, a Senegal-based analyst who recently traveled to Mali, told CNN there is concern that Abou Zeid transported a number of Western hostages with him after he left Timbuktu.

If Abou Zeid was indeed killed, the expectation is his group will retaliate.

"According to available accounts, he was somebody who generated fierce respect and loyalty in his men, so unless his fighting force has been severely degraded, there's a chance his group may lash out to avenge his death in the days and weeks ahead," Lebovich said.