Preparations are underway for a coalition of U.S. and Iraqi forces to retake Mosul from the Islamic State terror group. The United States has begun training Iraqi units, which will be ready by the spring or early summer to launch an offensive attack on the ISIS-controlled city, the top American commander in the Middle East told the Wall Street Journal on Thursday.

“If we did things alone or with some of the other allies on the ground, it could move faster. But the Iraqis have to do this themselves,” said Austin, adding he was undecided on whether to recommend U.S. ground troops in addition to the local Kurdish and Sunni fighters.

U.S. airstrikes reportedly targeted supply lines between Mosul and the ISIS stronghold in Syria on Wednesday and Thursday, Gen. Lloyd Austin told the Wall Street Journal. The Sunni militant group seized Iraq’s second-largest city in June. This strategic land grab expanded the ISIS stronghold in nearby Syria, allowing fighters and resources to flow across the border.

Austin, the head of the military’s Central Command, told the Wall Street Journal that the extremist group “is beginning to experience a manpower issue.” The international fight against the Islamic State has killed some 6,000 ISIS fighters and reclaimed about 300 square miles of territory in Iraq, according to Austin. However, Iraq’s vice president has dismissed these reports and claimed the Islamic State is a growing threat beyond the Arab world.

“ISIS is getting stronger,” Allawi said Thursday evening during a panel discussion at the world Economic Forum in Davos, Switzerland. “It’s not true that they have lost control in Syria and are losing control in Iraq. Let us face the facts as they are.”

The Islamic State insurgency controls large swaths of western and northern territory in Iraq and occupies almost one-third of Syria. U.S. officials told the Wall Street Journal much of the Kurdish-controlled areas in Iraq have been reclaimed. Just as many Sunni Syrians have joined ISIS forces to fight Syria’s President Bashar Assad and Shia Islam, many Sunni Iraqis have joined the group to fight their country’s Shia-led government.