( CNN ) Do you remember the talk about plans for Iraqi-led force to try to take back Mosul this spring ? Well , you might want to forget it . Nearly three months after a U.S. official said up to 25,000 Iraqis troops were expected to return to the key northern Iraqi city in April or May , a senior official in President Barack Obama 's administration said Thursday that Washington is `` not putting a timeframe on '' a possible invasion . It `` might be some time from now . Might be soon , '' another senior administration official said . Mosul has long been the big prize in the Iraqi government 's fight -- aided by a U.S.-led military coalition , which has carried out airstrikes for months -- to defeat ISIS . It has also long been a source of embarrassment , considering how it fell after Iraqi troops dropped their weapons , abandoned their posts and ran for their lives when militants arrived last June . The senior administration officials who talked to reporters Thursday stressed the Iraqis and their allies are making progress in their fight against the group that calls itself the Islamic State . In fact , officials insist that ISIS has been degraded substantially thanks to a combination of air power and ground combat . The biggest and most recent example of this came with the recapture a few weeks ago of Tikrit , the hometown of former Iraqi dictator Saddam Hussein that is located some 100 miles ( 160 kilometers ) north of Baghdad . Iraqi forces aided by Iranian-backed Shiite militiamen took that northern city , the same place where ISIS allegedly massacred Iraqi troops last year . Still , Mosul is n't Tikrit . For one thing , it has a lot more people -- about a million , one Obama administration official noted . And it 's more important not only to Iraq , but ISIS , meaning the terrorist group has all the more reason to go all-out to defend it . In some ways , the campaign for Mosul has begun , according to officials . There are no plans for U.S. combat troops involvement in an eventual operation , they say , but airstrikes have already targeted ISIS positions in the area . Just because the area has been softened up some from the air , though , does n't mean a full ground assault is imminent . Calling for `` patience , '' an administration official said that winning Mosul is a complex endeavor . It will `` take a lot of capacity , '' the official said , `` and some time to build . ''
Mosul official said in February that Iraqi troops could go into U.S. in April or May . Officials say now that there 's no timetable , an invasion could come sooner or later . They note that recapturing U.S. from ISIS could be a complicated endeavor .