The war against the Islamic State will likely require U.S. military advisers on the ground once the Iraqi forces decide to go on the offensive, a top U.S. military official said on Sunday.

Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey revealed in an ABC News interview that there will be situations in the future when ground troops will be needed to assist coalition air campaigns, but said that need has not yet emerged.

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He said tactics will likely change once the Iraqi military tries to retake Mosul, a northern Iraqi city IS captured in June.

He foresees Mosul needing a different kind of military advising and assisting because of the complexity of the fight that will be played out there.

Since the war against the Islamic State group began, President Barack Obama's administration has insisted it would not deploy American ground troops to assist in the fighting.

The U.S. top military adviser to the president had earlier testified before the Congress that if at some point he sees the need for U.S. boots in Iraq or Syria, he will make his recommendations to the president.

On Sunday's interview, he indicated that at one point, he might have to call in U.S. military officials to accompany Iraqi troops.

In what appears to be a disclosure of previously unreported details, Gen. Dempsey told ABC News' Martha Raddatz that he had to call two Apache helicopters this week to beat back IS fighters who were within 25 kilometers of seizing Baghdad airport.

He said the fighters were advancing toward the airport and the only available offensive tools at the time were the helicopters.

The aircrafts can carry out low-flying attacks at ground targets, but were also at risk of getting hit by surface-to-air missiles the group is known to possess, CNN reported.

The general said it was important that the airport remained out of the jihadist group's control.

TagsU.S. ground forces in Syria and Iraq