Iranian Kurdish female members of the Freedom Party of Kurdistan (PAK) sit with their weapons during a training session in Dibis, about 30 miles northwest of Kirkuk, Iraq. The world's top diplomats pledged today to support Iraq in its fight against Islamic State militants.

Sept. 15, 2014 Iranian Kurdish female members of the Freedom Party of Kurdistan (PAK) sit with their weapons during a training session in Dibis, about 30 miles northwest of Kirkuk, Iraq. The world's top diplomats pledged today to support Iraq in its fight against Islamic State militants. Safin Hamed/AFP/Getty Images

Iraqi forces battled Sunday to secure the country’s second-largest dam from Islamic State militants after U.S. airstrikes opened the way for a ground offensive, marking an expansion of the American bombing campaign to Anbar, the deadliest province for U.S. troops during the Iraq war.

Iraqi officials said the ground operation, spearheaded by Iraqi counterterrorism forces and backed up by allied tribesmen, troops and local police, was underway Sunday night in the vicinity of Haditha, about 150 miles northwest of Baghdad. There, militants have been attempting to seize control of the city’s strategic hydroelectric dam for months.

The attacks represented a sharp escalation of a U.S. military campaign that began Aug. 8, when President Obama ordered the Pentagon to intervene in Iraq to stem the rapid advance of the Islamic State, a Sunni extremist group that has swept across the north and west of the country.

Obama, in an interview Sunday on NBC’s “Meet the Press,” said it was time for stepped-up efforts against the Islamic State, which would require additional resources in the region.

“There’s going to be a military element to it,” he said. “And what I want people to understand, though, is that over the course of months, we are going to be able to not just blunt the momentum of ISIL. We are going to systematically degrade their capabilities. We’re going to shrink the territory that they control. And, ultimately, we’re going to defeat them.” The Islamic State until recently called itself the Islamic State of Iraq and the Levant, or ISIL.

The Haditha Dam is Iraq’s second-largest dam. (Doug Struck/The Washington Post)

While the Islamic State’s gains in and around the northern Iraqi city of Mosul have garnered more attention in recent months, the al-Qaeda splinter group with a reputation for brutality has also been consolidating its gains in Sunni-dominated Anbar since seizing control of the province’s two major cities in January.

Brig. Gen. Abdulwahab al-Saidi, the Iraqi special forces commander for Anbar, said the ground offensive was launched about 6 a.m. after U.S. jets began their campaign Saturday night. Iraqi special forces called in targets for U.S. airstrikes, he said.

The targets are outlying villages and towns controlled by the Islamic State, including Barwana, less than a mile outside Haditha on the eastern bank of the Euphrates River. From there, militants have been attempting to push north to the city and its dam, which stretches more than five miles across the river.

State media reported that Iraqi forces retook Barwana on Sunday afternoon, but the fluidity of the situation was underscored when the province’s governor, Ahmed al-Dulaimi, and a local leader toured the newly secured territory.

A mortar round landed about 15 feet from the two politicians as Saidi escorted them, the special forces commander said. Both men were injured by shrapnel and airlifted to Baghdad, but the injuries were not life-threatening, officials said.

The expansion of the U.S. strikes comes as the White House and Pentagon are putting together plans for a broader and more extensive military campaign against the Islamic State.

U.S. officials said Saturday’s airstrikes around Haditha were conducted under Obama’s previous authorization of action to prevent humanitarian disasters and civilian massacres. Had the dam fallen into extremist hands, they said, Shiite areas to the south would be at risk of flooding.

Like much of Anbar, the area around the dam was the scene of heavy fighting throughout the U.S. occupation, ending only when Sunni tribes in the area turned on al-Qaeda-

affiliated fighters and formed U.S.-supported tribal militias.

Sheik Ahmed Abu Risha, leader of the Sunni tribal Awakening movement that fought al-Qaeda alongside U.S. troops, called for a wider air campaign.

“We have been partners with the U.S. in fighting terrorists since 2006,” he said. “We need this support.”

But senior U.S. officials have stressed the need for a parallel political track, expressing hope that if Haider al-Abadi, Iraq’s prime-minister-designate, can form an inclusive government, some Sunni tribal leaders chafing under harsh Islamic State rule will rise up to fight the extremists.

Abadi has until Wednesday, when a 30-day constitutionally mandated deadline expires, to form a new government. A parliament session has been called for Monday evening, when lawmakers are expected to vote on the new lineup. If an agreement cannot be reached, it will deepen Iraq’s political crisis, forcing wrangling over a new candidate for prime minister.

Officials from U.S. Central Command, which oversees military operations in the Middle East, said that a mix of fighter and bomber aircraft carried out four attacks Saturday near the dam. The strikes, they said, destroyed five Humvees that had been captured by Islamic State militants from Iraqi security forces, another vehicle and a checkpoint.

U.S. officials said all of the aircraft exited the area safely. Central Command did not specify what types of aircraft were deployed or where they flew from.

U.S. warplanes returned to the vicinity of the Haditha dam Sunday, carrying out five more airstrikes and destroying several Islamic State Humvees and other vehicles, the officials said.

In remarks to reporters Sunday during a visit to Tbilisi, Georgia, Defense Secretary Chuck Hagel called the Haditha dam “a critically important facility” and said the strikes “are very much in line with what President Obama said were the guiding principles of military action in Iraq.”

Before Saturday, the U.S. military had conducted 133 airstrikes against Islamic State forces, all in northern Iraq. The bulk were carried out to help Kurdish and Iraqi government troops retake control of the Mosul dam, the country’s biggest, which holds back the Tigris River but had been captured by the Islamic State in early August.

Whitlock reported from Tbilisi, and Jaffe reported from Irbil, Iraq. Mustafa Salim in Baghdad and David Nakamura in Washington contributed to this report.