Preparations include selecting and training military units for the planned assault and cutting supply lines to ISIS fighters, General Lloyd Austin, head of the U.S. military's Central Command, told the Journal.
Later US declare spring is the best time to assault Mosul and show disagreement with Iraqi army to Mosul operation before spring.Mosul is the largest city in a self-declared ISIS caliphate straddling the border between northern Iraq and eastern Syria.
A senior Iraqi official told Reuters in November that Mosul was the focus of government efforts to defeat ISIS, because of the city's size and symbolic status.The U.S.-led forces have been conducting air strikes against ISIS targets in Iraq and Syria, including 16 since Wednesday that were centred on Mosul.
The Journal quoted Austin as saying that Iraqi forces must be ready before the offensive could begin.
"If we did things alone or with some of the other allies on the ground, it could move faster,” he told the newspaper. “But the Iraqis have to do this themselves.”.
Austin said he had not yet determined whether to recommend that U.S. ground troops accompany local units pushing into Mosul but added the military would “do what it takes,” the Journal said.
He told the paper that two Iraqi divisions were expected to lead the force fighting to retake Mosul. The newspaper quoted military officials as saying those forces would receive four to six weeks of U.S. training.
The Iraqi government recently asked for more weapons to help its military that partially collapsed in early stages of the fight against IS.
Meanwhile Air strikes have killed more than 6,000 ISIS fighters including half of the top command, according to U.S. officials.
U.S. intelligence estimates that ISIS – also known as Islamic State – has a total force of between 9,000 and 18,000 fighters.
Stuart Jones, U.S Ambassador to Iraq, said yesterday that more than 6,000 ISIS extremists had been killed in Syria and Iraq since air strikes began.
In the west of Iraq, Asharq Al-Awsat report that ISIS has converted more than 1,500 schools in Anbar province into military barracks, local sources said on Thursday.