Shiite fighters from Saraya al-Salam, who are loyal to Muqtada al-Sadr, gather in the holy city of Najaf before heading to the northern Iraqi city of Tikrit to continue the offensive against ISIS.

The United States is considering launching air strikes and could do so within days to back up Iraqi and Shiite forces battling to recapture Tikrit from the Islamic State of Iraq and Syria (ISIS) group, U.S. officials said Tuesday.

Top officials were weighing the move after the bid to retake Tikrit, the hometown of late-strongman Saddam Hussein, lost momentum in recent days.

The U.S.-led coalition has pounded ISIS with bombing raids in northern and western Iraq but has not taken part in the Tikrit operation, in which Iran has played a prominent role.

Possible air strikes near Tikrit are “being discussed at a high level” and could be days or weeks away, a U.S. official told AFP.

The delicate diplomatic and military aspects of such an option are still being worked out, said the official, who spoke on condition of anonymity.

In a shift, the coalition as of March 21 began providing intelligence from surveillance flights for the Tikrit assault, a senior coalition military official said earlier in Baghdad.

U.S. officials in Washington confirmed the account of “an eye in the sky” for the Iraqi troops and Iranian-backed Shiite militia.

President Barack Obama’s administration has insisted it does not coordinate military operations directly with Iran.

But the surveillance flights and discussions on possible U.S. air raids in Tikrit illustrate how Washington is moving towards greater indirect collaboration with Tehran, despite the intense distrust between the two arch-foes.

Obama’s deputies have said the military effort against the ISIS is coordinated through the Iraqi government, which works closely with both Iran and the United States.

Iraqi Army Staff Lieutenant General Abdulwahab al-Saadi, a top commander in Salaheddin province, of which Tikrit is the capital, told AFP on March 15 that coalition air support was needed there and that he had requested that the Iraqi defense minister ask for it.

The Pentagon said Tuesday it had not yet received a request from Baghdad for air power around Tikrit.

“If the Iraqis formally request US assistance, we would take a look at that,” Pentagon spokesman Colonel Steven Warren told reporters.

Nothing was being “ruled in or out,” he said.

Warren acknowledged that the Iraqi offensive on Tikrit had “stalled” even though ISIS militants were outnumbered and outgunned.

“The Tikrit operation frankly has not moved forward recently,” he said.

The difficulties of waging war in an urban setting was the main factor hampering the operation, he added.

The chairman of the U.S. Joint Chiefs of Staff, General Martin Dempsey, has said it is only a matter of time before ISIS is forced out of Tikrit, which is north of Baghdad.

The operation to take back Tikrit, which involves thousands of Iraqi soldiers, police and Shiite fighters, began on March 2.

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