BARWANA, Iraq (AFP) - US President Barack Obama has vowed to outline a long-awaited strategy against the Islamic State in Iraq and Syria (ISIS) on Wednesday, after Washington expanded its month-long air campaign to Iraq's Sunni Arab heartland.

The new strikes deepen Washington's involvement in the conflict and are a significant escalation for Obama, who made his political career opposing the war in Iraq and pulled out US troops in 2011.

Iraqi forces sought to capitalise on the strikes, which have largely been limited to the north since they began on August 8, attacking jihadists in the area and retaking the town of Barwana.

The operation and the expanded US strikes come at a critical time, with Iraq's parliament set to meet on Monday to vote on a new government after a lengthy and contentious process to select a premier-designate and potential cabinet members.

Obama, who has drawn flak for saying he did not have a strategy to combat ISIS, announced he will make a speech on Wednesday to lay out his "game plan" to deal with the jihadists.

"I'm preparing the country to make sure that we deal with a threat from" ISIS, Obama said in an interview on NBC's "Meet the Press". He said he would not announce the return of American ground troops to Iraq and would focus instead on a "counter-terrorism campaign".

"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," Obama said.

Arab League chief Nabil al-Arabi, meanwhile, said the bloc's 22 members had agreed to confront ISIS.

"The Arab foreign ministers have agreed to take the necessary measures to confront terrorist groups including" ISIS, he told reporters in Cairo, without explicitly supporting US calls for a coalition to back its air campaign.

American warplanes bombed fighters from the ISIS jihadist group on Sunday around the strategic Haditha dam on the Euphrates River in an area that the militants have repeatedly tried to capture from government troops and their Sunni militia allies.

The strikes destroyed four Humvees, four armed vehicles, two fighting positions and a command post, the US Central Command said in a statement.

Pentagon spokesman Rear Admiral John Kirby said in an earlier statement that "the potential loss of control of the dam or a catastrophic failure of the dam - and the flooding that might result - would have threatened US personnel and facilities in and around Baghdad, as well as thousands of Iraqi citizens".

Iraq moved on Sunday to take advantage of the strikes, launching a drive against militants in the Haditha area and regaining ground. "Joint forces backed by air support and tribesmen launched a wide attack to clear the areas surrounding the Haditha district," said security spokesman Lieutenant General Qassem Atta.

The troops and militia retook Barwana, east of Haditha, from the jihadists, who abandoned their weapons and vehicles in their retreat, a correspondent reported. The black ISIS banner was lowered from the town's main checkpoint and the Iraqi flag raised.

However, the victory was marred when a mortar round slammed into the town, wounding Anbar Governor Ahmed al-Dulaimi as well as Abdulhakim al-Jughaifi, the administrative official responsible for Haditha, and seven soldiers.

A suicide bomber then struck the convoy carrying Dulaimi to a nearby hospital, killing a soldier and wounding six.

The only previous US strikes against IS outside of northern Iraq were carried out in support of an operation by the army, Shiite militia and Kurdish fighters to break a months-long siege of the Shiite Turkmen town of Amerli, north of Baghdad.

Sustained US strikes could provide a major boost to pro-government forces in Anbar, where all of one city and chunks of another have been out of state control for more than nine months, along with other areas seized by militants since June.

Western governments have come under mounting pressure to take strong action against IS, which controls a swathe of neighbouring Syria as well as significant territory north and west of Baghdad.

The jihadist group has carried out a spate of atrocities in areas it controls, some of which it has videotaped and paraded on the Internet, including the beheading of American journalists James Foley and Steven Sotloff.

On Monday, Iraq's parliament is to meet to vote on a new government, a key test for the country. If a government is not agreed, this will mean a return to the start of the contentious process, leaving Iraq rudderless at a critical time.

There have been repeated calls from the international community, including the United States, for a broad-based government to help confront the militants. While this would ensure that all sides are represented, similar arrangements in the past have led to deadlock that has helped undermine government effectiveness.