Islamic State fighters are likely to put up a stiff defense of Mosul but eventually lose their grip and morph into an insurgency, a U.S. Army general said Wednesday.

Maj. Gen. Gary Volesky, commander of U.S. and coalition land forces in Iraq, said this transition from conventional combat to counter-insurgency is deemed so predictable that the U.S. training regimen for Iraqi security forces is already being adjusted to prepare them for insurgent threats.

Volesky, speaking to reporters at the Pentagon via video link from his headquarters in Baghdad, also disclosed that U.S. Army Apache helicopters have entered the battle for Mosul. He declined to provide specifics, citing the need to preserve operational security, but said they have been striking Islamic State targets at night. The mere presence of the Apaches on the battlefield has been a confidence booster for Iraqi soldiers, he said.

The Apaches, he said, can "see a long range at night" and strike targets from a great distance. "That's what they're doing," he said.

Volesky said some Islamic State forces already are giving up their positions in the outskirts of Mosul and pulling back into the city. He said he expects this trend to continue. They are then likely to attempt to block the entry of Iraqi forces into the city, using a "full-fledged conventional defense."

At some point, he predicted, the Iraqi forces will prevail, and at that point, "I expect they (Islamic State fighters) are going to go into insurgency mode."

"That's my assessment," he added. "That's what we're preparing the Iraqis for."

Earlier this month, a Canadian general who runs a portion of the coalition training of Iraqi security forces told reporters that retaking Mosul from the Islamic State would open a new, more dangerous phase of the counter-IS fight. Brig. Gen. Dave Anderson said the period between the fall of Mosul and the ultimate defeat of IS "is probably when it's most dangerous."

"Literally, what we've been talking about is how do we position police forces and minister of interior forces in order to be able to fight the enemy the day after Mosul and its new metastasized form," Anderson said Oct. 5.