Thousands of Iraqi troops backed by Iranian-trained Shiite Muslim militias pushed north Monday toward Tikrit, Iraq, marking a major offensive to wrest control of the strategic and heavily symbolic city from the militant group Islamic State.
The attack, involving more than 20,000 fighters along with air power, tanks and artillery, appeared to be the most concerted effort to date to expel the extremists from one of their major urban strongholds.
Helping to spearhead the assault were Shiite militiamen whose presence and ties to Shiite Iran could stoke sectarian tension tearing Iraq apart in what is likely to be a bloody thrust against a largely Sunni Muslim area. About 2,000 Sunni militia members were also lined up on the government side, authorities said.
Should the Shiite militias defeat the militants in Sunni-dominated Tikrit, they could be seen as an occupying force and may pose a problem for Prime Minister Haider Abadi's fragile 6-month-old government in Baghdad.
On Monday, Iran's semiofficial Fars News Agency reported that Gen. Qassem Suleimani, commander of Iran's elite Quds Force, was on hand at the battle scene outside Tikrit to "supervise and consult with the Iraqi commanders."
Iraq's Shiite militiamen are regarded as among the most effective forces at the government's disposal.
Whereas Iraqi troops retreated en masse last year in the face of Islamic State advances, Shiite militias helped defend Baghdad, the capital, and pushed back extremists allied with local Sunni factions. Islamic State, also known as ISIS or ISIL, is a Sunni fundamentalist group that views Shiites as apostates and Shiite Iran as a mortal enemy.
The Shiite militiamen, enraged at Islamic State's mass killings of Shiites, have been accused of revenge attacks on Sunni civilians in Iraq. Islamic State militants have executed hundreds of Shiite captives in grisly scenes uploaded to the Internet.
The operation to retake Tikrit has been dubbed "By Your Command O Prophet of God," reported the state news outlet Al Iraqiya.
Tikrit was the hometown of the late Saddam Hussein, the Sunni strongman who was deposed in 2003 in a U.S.-led invasion that helped usher Iraq's Shiite majority into power after decades of marginalization. Some Iraqi Sunnis view Hussein as a martyr who served as a bulwark against Shiite Iran and its co-religionists in Iraq.
Hussein launched a 1980s war against Iran that claimed hundreds of thousands of lives and included Iraqi chemical attacks on Iranians and Iraqi Kurds.
Tikrit remains a bastion of Sunni Muslims opposed to Shiite rule in Baghdad. Many Sunnis in Tikrit and elsewhere in Iraq sided with Islamic State forces when they swept through the area last year.
Suleimani, a shadowy figure whose image invariably pops up in sundry Middle Eastern battlefields and proxy wars, has been a longtime nemesis of the West. He has worked in concert with the forces of Hezbollah, the Iranian-backed Shiite militant group in Lebanon, and with those of Syrian President Bashar Assad, who has defied calls from Washington and its allies that he step down as Syria's civil war nears its fifth year.
In Iraq, however, Suleimani and the Iranian forces oppose Islamic State, as does the United States. Neither Iran nor the U.S. — both longtime adversaries — wants to admit publicly to such an alliance of convenience.
Since the summer, a U.S.-led coalition has launched more than 2,000 airstrikes in Iraq and neighboring Syria against Islamic State, which President Obama has vowed to "degrade and ultimately destroy." Several thousand U.S. trainers and advisors are in Iraq.
But the Pentagon said Monday that no air power was being provided to Iraqi forces advancing on Tikrit.
Col. Steve Warren, a Pentagon spokesman, said the U.S.-led military coalition is willing to provide intelligence and other assistance for the assault if Iraqi commanders request it.
"I'm not going to speak to the details of Iranian involvement," he said. "But we know [Islamic State] is of great concern to Iran."
Islamic State overran Tikrit in June as its fighters swept through much of the Sunni heartland of northern and central Iraq. The group formed alliances with Sunni fighters in Tikrit and elsewhere, capitalizing on disenchantment with the Shiite-led administration in Baghdad.
The bid to recapture Tikrit, about 100 miles north of Baghdad along the Tigris River, looms as a major challenge.
Several army attempts to recapture the city last year ended in disaster. Pro-Baghdad forces suffered hundreds of casualties, and many troops taken prisoner were later reported executed by Islamic State militants.
The attack could offer a preview of a much-anticipated offensive expected this year in an attempt to recapture a larger objective: the city of Mosul, 140 miles up the Tigris from Tikrit. Islamic State also controls Mosul, one of Iraq's largest cities and a longtime cultural and economic hub. Retaking Tikrit and Mosul probably would involve street-to-street warfare, analysts say.
Human rights activists and others have voiced grave concerns about possible civilian casualties as Iraqi forces try to retake Tikrit and other areas. Previous government bombardments of Tikrit, Mosul and other zones have resulted in numerous civilian deaths, according to human rights monitors and others.
Much of the civilian population is believed to have fled Tikrit, once home to 250,000 people.
But government officials charged that Islamic State forces were preventing civilians from leaving Tikrit.
"The enemy is using civilians as human shields," said Mowaffak Rubaie, an Iraqi parliament member and former national security advisor. "We have seen women, children and elderly trying to escape the city toward the west, but the enemy is not letting them through."
Islamic State controls vast stretches of Syria and Iraq despite U.S. airstrikes and a wide array of ground forces aligned against it, including Kurdish fighters, Iraqi and Syrian troops, allied militiamen and some of the factions fighting the Syrian government.
Islamic State strongholds are concentrated in mostly Sunni areas of northern and western Iraq, as well as in northern and eastern Syria.
Times staff writer McDonnell reported from Beirut and special correspondent Bulos from Amman, Jordan. Staff writer W.J. Hennigan in Washington and special correspondent Ramin Mostaghim in Tehran contributed to this report.