Military vehicles of the Iraqi Special Operations Forces (ISOF) gather during a battle with Islamic State militants in Qadisiyah neighborhood north of Mosul, Iraq, December 14, 2016.

Iraqi forces battling to retake Islamic State’s last major stronghold – Mosul – have entered a planned operational refit, a top U.S. general in the international coalition backing Baghdad said, the first significant pause of the campaign.

Elite soldiers have retaken a quarter of the northern city, but their advance has been slow and punishing. Several thousand Iraqi federal police were redeployed from the southern outskirts last week to reinforce the eastern front.

They are part of a 100,000-strong alliance which launched a campaign on Oct. 17 that has become the biggest in Iraq since the 2003 U.S.-led invasion that toppled Saddam Hussein.

"This is an operational refit. This sets the conditions for continued progress by ISF (Iraqi security forces) and their plan and their operation to liberate Mosul," U.S. Air Force Brigadier General Matthew Isler, deputy commander for the coalition’s air forces told Reuters by phone from Baghdad on Wednesday.

The refit follows 65 days of "going at this at an operationally high tempo the entire time", he said, and includes repairing vehicles, resupplying ammunition and preparing forces for the next stage.

"There is a lot of activity going on. You would see a busy beehive … of them in their operational refit," he said. "They are going to resume soon and the ISF are driving that timeline."

Forces from Iraq’s counter-terrorism service (CTS), which has spearheaded most major battles against Islamic State since the army and police dropped their weapons and fled in 2014, are still making advances in Mosul but at a much slower pace than at any other time in the battle.

While the Iraqi government does not provide casualty figures for its military, concerns are growing about the toll of CTS deaths. Isler said the refit was vital to long-term success.

"What really matters in a campaign is progress over time. Every day is different and has those unique challenges. It also means that in each of those days and challenges you have to sustain your forces," he said.

CTS has made some small advances in eastern Mosul recently, but usually rosy reports from the military’s war media cell this week have said only: "No changes on all axes".

Iraqi authorities have increasingly restricted the foreign news media’s access to the battle fronts and areas retaken from Islamic State in and around Mosul, making it difficult to confirm their accounts.

Defeating Islamic State in Mosul, the biggest city it controls in Iraq or neighbouring Syria, would be a crushing blow to the self-styled caliphate it declared in large parts of both countries 2-1/2 years ago, and might see it revert to more covert militant operations in Iraq.

"I don’t think anyone can deny momentum is with Iraq. The ISIL defeat is inevitable. Even Daesh knows it, they are not playing to win and they are just trying to buy time," said Isler, using two acronyms for Islamic State.

(Editing by Louise Ireland)