Members of Iraqi security forces coming from the city of Samarra, north of Baghdad, drive towards the al-Dawr area, south of Tikrit, to launch an assault against the Islamic State on Feb. 28. (Ahmad Al-Rubaye/AFP/Getty Images)

Iraqi forces backed by Shiite militiamen and Sunni tribal fighters opened a large-scale operation Monday seeking to ­retake the Islamic State-held city of Tikrit, a critical steppingstone for wider attempts to reclaim territory in northern Iraq.

The offensive — announced on Iraqi state television — marks the third attempt by government forces to regain control of the city from the Islamic State militants, who seized it in June.

Tikrit, about 110 miles northwest of Baghdad and the home town of Saddam Hussein, is a strategic foothold along a major highway linking the capital and Mosul, the largest city in northern Iraq. Mosul also is held by the Islamic State.

Iraqi officials said more than 10,000 fighters — including soldiers, federal police, and Sunni and Shiite factions — attacked ­areas around Tikrit from three sides. They were backed by artillery fire and airstrikes from Iraqi fighter jets, officials said.

[Watch: Islamic State smashes artifacts in Mosul]

“This is only the first stage of the battle,” said Aday Thanoon, a council member in Salahuddin province, where Tikrit is located.

A spokesman for the U.S.-led coalition that has been hitting Islamic State targets in Iraq since August said that it had not conducted airstrikes in the Tikrit operation and that Iraqi authorities had not requested such assistance.

Although coalition officials said Iraqi requests would be considered, the operation presents a quandary for the Obama administration, which has steered clear of interacting with Shiite militias and with Iranian military figures, all of whom appear to be playing a big role in the battle for Tikrit.

Iraq did not provide the United States with advance notice of the Tikrit operation, said a U.S. official, speaking on the condition of anonymity to discuss communications with the Iraqi government.

Iraqi officials said troops “liberated” villages about 15 miles south of Tikrit on Monday afternoon. Pro-government forces encountered improvised explosive devices, snipers and booby-trapped houses on the way.

“The operation is not going to be easy,” said ­Jassim al-Jubara, the head of the area’s security committee.

As Jubara spoke by telephone Monday, a man could be heard informing him that his 24-year-old nephew had been killed on the battlefield.

Iraq's armed forces, backed by Shiite militia, attacked Islamic State strongholds north of Baghdad in an offensive to retake the city of Tikrit. (Reuters)

“Praise God,” Jubara responded. “We are all sacrificing for Iraq.”

Tikrit and surrounding areas are populated by Sunnis, who view the Shiite-led government in Baghdad with suspicion. The presence of Shiite forces — which have close ties to Shiite power Iran — in the offensive could be a test of Sunni cooperation in the region.

In Tikrit last summer, Islamic State militants massacred as many as 1,700 Iraqi Shiite soldiers at Camp Speicher. Many Iraqi Shiites believe Sunni tribesmen helped kill the troops. Rights groups, meanwhile, have accused Shiite militias of committing abuses against Sunni residents they suspect of aiding the militants.

Iran’s Fars News Agency said Monday that the offensive is being assisted by members of the Iranian Revolutionary Guard Corps, including the commander of the elite Quds Force, Maj. Gen. Qasem Soleimani.

Mustafa Salim in Baghdad and Missy Ryan and Brian Murphy in Washington contributed to this report.