At Iraq’s request, the U.S. has begun airstrikes in Tikrit in support of a stalled Iraqi ground offensive to retake the city from Islamic State fighters, a senior US official said.

The airstrikes were “ongoing,” the official said without providing details. The official spoke on condition of anonymity because the attacks had not yet been officially announced.

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

Iraq began the Tikrit ground offensive in early March without requesting U.S. air support, even as it welcomed help from Iran.

In an address to the nation yesterday evening, Prime Minister Haider al-Abadi predicted success in Tikrit but did not say the U.S. was providing airstrikes.

“We have started the final phase of the operation in Tikrit,” he said. “You will liberate your ground, not anyone but you,” he said, in a speech to the Iraqi people.

Al-Abadi praised all the groups involved in the battle against the Islamic State group, including the so-called Popular Mobilization Forces, which the U.S. calls Iranian-backed militias, the Sunni tribes and coalition forces. But he fell short of confirming that the coalition is playing a direct role in Tikrit.

US airstrikes in Tikrit raise highly sensitive questions about participating in an Iraqi campaign that has been spearheaded by Iraqi Shiite militias trained and equipped by Iran, an avowed US adversary.

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 US air support when it launched the offensive in early March.

Recently, the offensive has lost momentum. Colonel Steve Warren, a Pentagon spokesman, said yesterday the Iraqi forces have encircled Tikrit but not yet made significant inroads into the heavily defended city limits.

“They are stalled,” he said.

The U.S. has hundreds of military advisers in Iraq helping its security forces plan operations against the Islamic State, which occupies large chunks of northern and western Iraq. But the U.S. as said it is not coordinating any military actions with the Iranians.

Warren said that at Baghdad’s request the U.S. began aerial surveillance over Tikrit in recent days and is sharing the collected intelligence with the Iraqi government.

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