The Pentagon gave orders for U.S. and coalition forces to begin airstrikes to help Iraqi forces retake Tikrit, a senior U.S. defense official confirmed to Fox News on Wednesday.

Col. Steve Warren, a Pentagon spokesman, said the Iraqi government requested coalition support and that operations were ongoing Wednesday. A statement from the Combined Joint Task Force, the U.S. military command overseeing operations in Iraq, said the caolition was also providing intelligence and were assisting Iraqi Security Forces headquarters in the fight against the Islamic State, also known as ISIS, or ISIL.

An Associated Press reporter in Tikrit reported hearing warplanes overhead late Wednesday, followed by multiple explosions.

The U.S. and Iraq had been discussing airstrikes in support of a stalled Iraqi ground offensive against a dug-in ISIS force in the northern city, U.S. officials said earlier Wednesday.

The CJTF said Wednesday afternoon that Iraqi forces have ISIS in Tikrit encircled, but Warren said they have not yet made significant inroads into the heavily defended city limits.

"They are stalled," he said.

The prospect of U.S. airstrikes in Tikrit raises highly sensitive questions about participating in an Iraqi campaign that has been spearheaded by Iranian-backed Iraqi Shiite militias. Iran has provided artillery and other weaponry for the Tikrit battle, and senior Iranian advisers have helped Iraq coordinate the offensive. Iraq pointedly did not request U.S. air support when it launched the offensive in early March.

The U.S. has said it is not coordinating any military actions with the Iranians.

Warren, the Pentagon spokesman, said earlier Wednesday that at Baghdad's request the U.S. had begun aerial surveillance over Tikrit and was sharing the collected intelligence with the Iraqi government.

The spokesman said the Iraqis, who initially said they did not need American air power in Tikrit and were satisfied with their partnership with Iran, are discovering how difficult it can be to carry out ground operations in an urban area.

"I think it's important that the Iraqis understand that what would be most helpful to them is a reliable partner in this fight against ISIL," Warren said.

Fox News' Jennifer Griffin and The Associated Press contributed to this report.