US has more work to do to prepare an air base in northern Iraq before Mosul takeover can happen.
The number of Isis combatants in Iraq and Syria has been decimated by military campaigns, leaving as few as 15,000 to fight, according to a senior US commander.
Mr MacFarland claimed 45,000 enemy fighters are no longer on the front line after US backed operations.
The new figure of Isis fighters has shrunk from earlier approximations of between 19,000 and 25,000.
The US commander said the quality was of the fighters in combat was decreasing.
Forces with US support in Iraq and Syria were advancing, Mr MacFarland claimed. He said: “The enemy is in retreat on all fronts,” AP reported.
“All I know is when we go someplace, it’s easier to go there now than it was a year ago. And the enemy doesn’t put up as much of a fight,” he said.
US -backed opposition forces in Manbij, Syria claim to be in control of 90 per cent of the city.
Many of the homes and buildings in the city have been destroyed, Al Jazeera reported.