Turkish soldiers patrol as Islamic militants fight Kurdish forces to the west of Kobani, Syria, at the Turkey-Syria border near Suruc, Turkey, September 30, 2014. Burhan Ozbilici/AP Turkey is deploying over 100 military personnel in Iraq's Mosul region in order to help train anti-ISIS fighters, Reuters reports, citing a Turkish security force.

"Turkish soldiers have reached the Mosul Bashiqa region. They are there as part of routine training exercises. One battalion has crossed into the region," the source told Reuters.

However, the source refused to disclose how many Turkish soldiers are ultimately being deployed into Iraq.

According to security sources who spoke to CNN Turk, 130 troops are entering into the Mosul region to provide training to the Kurdish Peshmerga.

The deployment of fresh Turkish soldiers into the Mosul region to train Peshmerga follows a training regiment for the Kurdish forces that was already in place. A Peshmerga spokesman told Reuters on November 22 that Turkish soldiers had begun training the Kurds three weeks earlier in various locations throughout northern Iraq.

The timing and location of the deployment of Turkish forces into Iraq is still noteworthy. The news comes amid accusations from Russia that Turkey is participating in and facilitating ISIS's trade in oil, providing the group with millions of dollars in monthly revenue.

The location of the training, which is happening in the Bashiqa region, is also important. Bashiqa Mountain is within 20 miles of Mosul and has been used as a training area for various anti-ISIS factions, including the Peshmerga and Yazidi militias, al-Monitor reports.

The presence of Turkish trainers so close to Mosul reflects the current battle lines in the region for ISIS and the Kurds. Even so, the flow of Turkish trainers into the region could also represent a more immediate effort to retake Mosul, the second-largest city in Iraq and the largest city in ISIS's "caliphate."

As Foreign Policy reports, the Kurdish recapture of Sinjar from ISIS in November was a possible first step toward an eventual assault on Mosul. By capturing Sinjar, the Kurds made it more difficult for ISIS to connect Mosul to its de facto capital of Raqqa in Syria.

"Taking back southern Sinjar could be the start of a larger operation,” Christine van den Toorn, a researcher at the American University of Iraq in Sulaimaniya, Iraq, told FP. “Taking Sinjar and moving east to Tal Afar and then up to Mosul” would be a likely military strategy, she added.

And any potential military action against Mosul would seriously threaten ISIS's claims to a caliphate. The city is Iraq's second largest, and it's where ISIS first declared its establishment of a caliphate in June 2014. Losing the city would be a major blow to the group, and particularly to its claims of political legitimacy.

An assault on Mosul also wouldn't necessarily require anti-ISIS forces to reclaim the entirety of the city in a single campaign.

"They don't have to take the whole thing," Michael Pregent, a former US Army intelligence officer, told Business Insider in April 2015. "They just to be able to take the airfield in Mosul or key bridges between east and west Mosul. That would be enough to deconstruct the narrative of the capital of the caliphate in Iraq as being under the control of ISIS ... if you're able to bomb ISIS targets from an airfield in the ISIS capital of Iraq, it's a very big deal."

Armin Rosen contributed to this report.