Story highlights A push to retake Tikrit stalled as ISIS repositioned its forces around the city

Spokesman: Iraq's leader requested help because coalition has "advanced" capabilities

Leaders of predominantly Shiite militia fighting in area had resisted such intervention

(CNN) U.S.-led warplanes continued to hammer ISIS positions around the pivotal Iraqi battleground city of Tikrit, stepping in at the Iraqi Prime Minister's request to get at what a spokesman called "difficult targets."

The U.S. military announced Thursday that it and its allies conducted 17 airstrikes around Tikrit, going after three ISIS checkpoints, two bridges, two staging areas and other targets such as a roadblock and a "command and control facility."

The idea is that this aerial bombardment will pave the way for Iraqi forces to go in and take control on the ground.

"The ongoing Iraqi and coalition airstrikes are setting the conditions for offensive action," said Lt. Gen. James L. Terry, commanding general of the U.S.-led coalition.

Iraqi forces have tried multiple times to win back Tikrit since the group, which calls itself the Islamic State, conquered the city in June as part of its campaign to amass an expansive Islamic caliphate. And each time, so far, they've failed.