Story highlights Commander of US troops in the Middle East predicts "tough fight" ahead in Mosul, Iraq

Called clashes between US allies, Turkey and Syrian Kurds, "unhelpful"

Washington (CNN) A top US general said Tuesday that ISIS fighters defied their leader's orders to fight to the death in a recent battle, instead retreating to the north.

Gen. Joseph Votel, the commander of US forces in the Middle East, said that the refusal to follow orders occurred during the battle for the recently liberated town of Manbij, Syria.

ISIS leader Abu Bakr Al-Bagdadi told fighters in Manbij "to fight to the death" and "they didn't follow his direction," according to Votel, questioning how much command and control ISIS leadership has over its forces.

Still, he said that ISIS, also know as ISIL, has a "strong network" that relies on "guidance from centralized leadership."

Votel, speaking to reporters at the Pentagon, said he thinks that the Iraqi security forces "are on track" to recapture the key city of Mosul from ISIS by the end of 2016. But he warned that Mosul will be "a tough fight" now that the coalition is "into the heart of the caliphate."

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