The offensive to take back Tikrit - the home town of executed dictator Saddam Hussein - has stalled over the past week with jihadists defending their positions with homemade bombs.
"I can confirm that the government of Iraq has requested coalition support for operations in Tikrit," Pentagon spokesman Colonel Steven Warren said yesterday.
An Iraqi special forces lieutenant colonel told AFP: "International coalition forces bombed four areas in the centre of Tikrit city."
Strikes hit an area around a palace compound area and near the Tikrit hospital, he said.
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Over the weekend, US aircraft - including drones - began carrying out surveillance flights to support the Tikrit operation on the ground against the IS militants.
Other countries in the US-led coalition were taking part in the air strikes, officials said.
"These strikes are intended to destroy ISIL strongholds with precision, thereby saving innocent Iraqi lives while minimising collateral damage to infrastructure," said Lieutenant General James Terry, who oversees the command in charge of the US war effort.
Instead, long-time US foe Iran has played a prominent role, providing artillery and deploying advisers to the Iraqi Shiite militias also taking part in the operation.
But the assault has become bogged down, even though the Iraqi forces far outnumber the IS militants.
US officials and military officers made no secret of their view that Iraq had made a mistake in not asking for American air power from the start and relying solely on Iran's assistance.
At a Pentagon briefing earlier yesterday, spokesman Colonel Steven Warren said the US-led coalition was the most capable and "reliable" partner for Iraq.
He said the Iraqis had made confident predictions when the offensive on Tikrit was launched earlier this month, but he said "urban combat is difficult and slow" and the coalition had unmatched military power to offer.