The U.S. is now considering launching airstrikes against Islamic State (ISIS, ISIL) targets inside Mosul for months prior to sending in Iraqi ground troops to recapture the city.

“Under the evolving plan, the U.S. would use its air power in the coming months to further isolate Mosul and weaken the hold of Islamic State fighters on the city. Under this approach, U.S. airstrikes would be focused on picking off Islamic State leaders to undermine their ability to command and control their forces,” reported The Wall Street Journal (WSJ) on Friday.

Unnamed U.S. officials told WSJ that “the on-the-ground fight to retake Mosul isn’t likely to start until the fall at the earliest, after an intensified air campaign to target Islamic State leaders and cut off supply lines in and around the city.”

Kurdish media service Rudaw reported on Sunday that Turkey has decided to help retake Mosul, Iraq’s second largest city, which is still under the control of ISIS.

Asil Nujaifi, the exiled governor of Mosul, told Rudaw that Turkey “has agreed to send weapons and supplies for recapturing Mosul.”

Initially, the U.S. plan was to launch a spring ground offensive to drive ISIS out of Mosul.

An official from U.S. Central Command (Centcom), speaking on condition of anonymity, told reporters on February 19 that the U.S. and Iraq would start a campaign to liberate Mosul by April or May.

“I really doubt it is going to happen that soon,” one U.S. military official told The Daily Beast on condition of anonymity after the Centcom official revealed the Mosul plan to reporters.  “And if it does, it will take months.”

Anonymous U.S. military officials are now telling The Journal that it will take “many months” to prepare Iraqi’s best military units to successfully retake Mosul so they are rethinking the original plan.

“When we feel that the Iraqi forces are ready to go and win decisively, we will go and advise the Iraqis to begin the operation,” a military official told WSJ.

Unnamed officials also told The Journal that “the U.S. believes that a force of around 20,000 fighters will be needed to liberate and hold Mosul.”

Last Friday, Rear Adm. John Kirby, the Pentagon press secretary, told reporters, “We’re not going to be able to go, nor do we want to go any faster than the Iraqis are ready to go.”

Kirby would not rule out an April offensive in Mosul, saying there are no timelines. He acknowledged that any operation to retake Mosul would involve a tough fight.