Smoke rises at Islamic State militants' positions in the town of Naweran near Mosul, Iraq, Oct. 20, 2016. REUTERS/Zohra Bensemra

Leaders and militants of the Islamic State group are fleeing Mosul as U.S.-led coalition forces are intensifying their offensive to retake the group's last major stronghold in Iraq. However, reports said Wednesday that ISIS leader Abu Bakr al-Baghdadi is believed to be holed up with the group's bombmaker Fawzi Ali Nouimeh in Mosul.

Senior Kurdish official Hoshiyar Zebari reportedly said that his forces had “solid” intelligence that al-Baghdadi was still in Mosul, even as U.S. officials said that leaders of the group were moving out of the city. Kurdish fighters said that they have launched a large-scale operation east and north of Mosul, as part of an offensive to retake the city from ISIS.

French President François Hollande said early Thursday that authorities have evidence that ISIS militants are fleeing Mosul, giving rise to concerns about their regrouping in Raqqa, Syria. Hollande urged that necessary measures should be taken to stop the militants from entering Syria.

On Wednesday, U.S. Army Maj. Gen. Gary Volesky, who heads the land component of the U.S.-led coalition against ISIS, said that they have noticed movement out of Mosul.

"We are telling Daesh (Arabic acronym for ISIS) that their leaders are abandoning them. A lot of foreign fighters we expect will stay as they’re not able to exfiltrate as easily as some of the local fighters or local leadership, so we expect there will be a fight,” Volesky reportedly said. “All I can tell you is there are fewer Daesh fighters today than there were yesterday and there will be fewer tomorrow than there are today."

Al-Baghdadi's presence in Mosul would reportedly mean that the remaining 3,000 fighters in the city will increase their support to defend the last ISIS stronghold in Iraq. While speculation continues about al-Baghdadi's whereabouts, Iraqi forces are advancing toward Mosul at a much faster pace than planned.

"The forces are pushing towards the town more quickly than we thought and more quickly than we had programmed in our campaign plan," Iraqi Prime Minister Haider al-Abadi told senior officials in Paris in a video conference call.

Iraqi forces have retaken several villages south and east of Mosul since beginning the offensive late Sunday. Among the villages is Qaraqosh, which lies about 10 miles from Mosul and was once Iraq's largest Christian town.