And while officials won't publicly confirm it, there have been several meetings to begin to determine if more troops are needed for the upcoming battle for Iraq's second-largest city and what those troops might do to affect the battle.
The top U.S. commander in Iraq, Lt. Gen. Sean MacFarland, by all accounts has not yet asked for more troops, several U.S. officials told CNN.
"He engaged with dialogue up through his chain of command where he thinks there might be an area where we might require an increase in capability, and I use that word 'capability' because it can be a rash of forms," said British Army Maj. Gen. Doug Chalmers, deputy commander for strategy in the U.S.-led coalition, in a news briefing for Pentagon reporters.
Chalmers noted additional troops, if sent, could deal with air support, reconnaissance and surveillance as well as training, advising and assisting Iraqi forces. The issue of troop levels is one that is constantly being reviewed by the military, but these latest discussions center on what, if anything, is needed to support an Iraqi assault on Mosul.
Several defense officials have told CNN they cannot predict at this point when an Iraqi assault could begin, but it's generally thought to still be some months off. There are ongoing Mosul planning meetings with top Iraqi officials, and when a plan is set, further, more specific discussions about additional forces could begin.
Iraqi forces currently are fighting their way north toward Mosul and beginning to try to retake villages and towns in order to isolate the city before any plan is implemented for a direct assault. Mosul remains ISIS' major stronghold in Iraq.
MacFarland currently has legal authority to request more troops without having to get fresh White House approval. The current limit on the number of troops in Iraq is 4,087, but there are only about 3,600 on any given day. So he could request about another 400 without having to get President Barack Obama's permission and perhaps not even make a public announcement of more troops unless he wanted to request more than the current limit.
Troop levels in Iraq remain highly imprecise, however, because there are dozens of additional forces there under temporary orders that do not count against the 4,087 limit.
One official said the current 400-troop "cushion" that could be sent is essentially being kept as a hedge in case more troops are in fact needed for a Mosul assault.
Defense Secretary Ash Carter has spoken about being willing to approve more "accelerants," such as troops for the fight against ISIS, so any request from MacFarland would be likely to be approved if it can be demonstrated the troops are needed, officials said.
But one official noted that MacFarland has to "maximize what he's got before asking for more." The U.S., for example, would like to see the Iraqis take more advantage of U.S. Apache helicopter gunships in attacking ISIS ground targets.
The other challenge in answering the question of whether more troops are needed is that as Iraqi forces continue to move north towards Mosul, ISIS itself is reconfiguring. Some ISIS troops appear to be retreating into villages and towns along that route. And intelligence indicators show ISIS is reinforcing positions in Mosul with more fighters.
But that also consolidates ISIS into a less-dispersed geographic area. That is a consideration in determining if more U.S. military advisers are needed if the fighting remains in consolidated areas.