The U.S.-led anti-Daesh effort will increase the number of troops in Iraq that will train more Iraqi fighters ahead of a Mosul operation, a coalition spokesman said Wednesday.

"That's really the next step in generating the amount of combat power needed to liberate Mosul," said Col. Steve Warren.

"We know we will need more brigades to be trained, we'll need more troops trained in more specialties." Speaking via video conference from Baghdad, he said that although the number of new trainers had not yet been worked out, he would estimate it at hundreds.

News of the additional trainers was first given late Tuesday by Defense Secretary Ashton Carter while en route to Paris where he will meet his counterparts from France, Italy, the Netherlands, Australia, Germany and the UK to discuss the anti-Daesh campaign.

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

He said Iraqi forces retook territory from Daesh and are moving toward Mosul, the militant group's stronghold, where there will be a need for "ground forces that can seize territory", and "police forces that can keep security".

The troops to be deployed will be based in the existing training bases in Besmaya and Taji, two bases near Baghdad, as well as Al-Assad base in Anbar province, according to Warren.

There are currently approximately 3,500 U.S. trainers in Iraq training the Iraqi army as well as Sunni tribal fighters and Kurdish peshmerga forces.

Since last May the U.S. has provided basic combat training for 16,715 Iraqi and peshmerga forces and various specialized training programs for thousands more, the Pentagon said.