U.S. military officials are in high-level talks with the Iraqis about potentially sending hundreds of additional troops to Iraq for training and supporting the upcoming invasion of the Islamic State group's stronghold in Mosul.

"Prime Minister [Haider al-Abadi] has asked for additional enablers and so we're working now with him to figure out exactly what that looks like," said Army Col. Steve Warren, a Baghdad-based spokesman for the Defense Department.

Warren said the number would be "not thousands, hundreds" and also said some of those troops might be from allied nations.

Speaking to reporters Wednesday, Warren said the Iraqis will likely need at least eight combat brigades for the invasion of Mosul, Iraq's second largest city. Additional trainers would help prepare the Iraqis for the Mosul operation, which some military officials say may not begin until next year.

The current American-led support mission has trained about three Iraqi brigades during the past year, and U.S. officials expect two brigades from the Kurdish peshmerga forces to join the fight. The Iraqis will need "several more brigades" for a Mosul operation, Warren said.

Defense Secretary Ash Carter was in Paris on Wednesday to meet with allied defense ministers about the anti-ISIS mission. Carter also said the number of U.S. troops on the ground may increase from its current force of about 3,600.

"We're certainly open to that," Carter told reporters traveling with him to Paris on Tuesday.

"The president has indicated wherever there's additional opportunity to make a difference, according to the strategy, we'd be willing to do that," Carter said.

"I expect the number of trainers to increase, and also the variety of the training they're giving," Carter said.

Carter in December offered to send a new cadre of ground-level American combat advisers for the Iraqi army's brigade-level headquarters as well as U.S. attack helicopters for close-air support.

But the Iraqi government so far has declined that offer, in part due to the pro-Iranian factions inside the Baghdad government who opposed expanding the U.S. military role.

Carter said he hopes other countries, especially Sunni Muslim countries, will also offer to send troops for the train-advise-and-assist mission in Iraq and possibly Syria.

"They all need to be part of the coalition, too, including the coalition military campaign. ... I have long said that Arabs and Sunni Arabs need to get in the game," Carter said.