U.S. air strikes target insurgents near Iraq's Haditha Dam

Obama has branded Islamic State an acute threat to the West as well as the Middle East and said that key NATO allies stood ready to back Washington in action against the well-armed sectarian force, which has seized expanses of northern Iraq and eastern Syria and declared a border-blurring religious caliphate.

The leader of a pro-Iraqi government paramilitary force in western Iraq said the air strikes wiped out an Islamic State patrol trying to attack the dam - Iraq's second biggest hydroelectric facility that also provides millions with water.

"They (the air strikes) were very accurate. There was no collateral damage ... If Islamic State had gained control of the dam, many areas of Iraq would have been seriously threatened, even (the capital) Baghdad," Sheik Ahmed Abu Risha told Reuters.

The aerial assault drove Islamic State fighters away from the dam, according to a police intelligence officer in the vast western province of Anbar, a hotbed of Islamist insurgency.

The U.S. military said in a statement that the strikes destroyed four IS Humvees, four IS armed vehicles, two of which were carrying antiaircraft artillery, an IS fighting position, one IS command post and an IS defensive fighting position. All aircraft left the strike areas safely, the Pentagon said.

The strikes were Washington's first reported offensive into Anbar since it started attacks on Islamic State forces in the north of Iraq in August.

Almost three years after U.S. troops withdrew from Iraq and 11 years after their invasion that toppled Saddam Hussein, the war on Islamic State is drawing Washington back into the middle of Iraq's power struggles and bloody sectarian strife.

U.S. Defense Secretary Chuck Hagel said the strikes on the Sunni Muslim insurgents had been carried out at the request of the Shi'ite Muslim-led central government in Baghdad.

“If that dam would fall into (Islamic State's) hands or if that dam would be destroyed, the damage that would cause would be very significant and it would put a significant, additional and big risk into the mix in Iraq,” Hagel told reporters during a trip to Georgia’s capital, Tbilisi.

OBAMA VOWS TO REPEL, DEFEAT ISLAMIC STATE

Obama said on the weekend he would explain to Americans this week his plan to "start going on some offense" against Islamic State. "We are going to be a part of an international coalition, carrying out air strikes in support of work on the ground by Iraqi troops, Kurdish troops, he said in an NBC TV interview.

"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 'em."

The six-month-old battle for control of the Haditha Dam has been a rare case of cooperation between local Sunni tribes and the Shi'ite-led Iraqi military. The Juhayfa tribe in Haditha has a long-standing fight with the Islamic State, which split with its parent organization al Qaeda last year.

Anbar is complicated terrain for the Americans as they seek to root out Islamic State, since Sunnis fighting on behalf of the Baghdad government are the exception to the rule.

The large desert province, bordering Syria, Jordan and Saudi Arabia, has been at war with Baghdad since last December when then-Prime Minister Nuri al-Maliki sent troops to raze an anti-government demonstrators' camp.

That sparked a tribal revolt against Maliki whom Sunnis accused of isolating them with indiscriminate arrests. Islamic State fighters took advantage of the chaos to muscle in and become the dominant force among Sunnis.

The fighting there, which has displaced 430,000 people since January, strengthened Islamic State ahead of its lightning blitz this summer across the north of Iraq, also threatening the semi-autonomous, Western-backed enclave of Kurdistan.

Thriving on Maliki's sectarian-motivated alienation of Sunnis, Islamic State committed wide-scale atrocities against Shi'ites, Christians and other non-Sunnis this summer as the Iraqi army imploded in the face of the insurgents' advance.

Since June, Islamic State has massacred hundreds of soldiers outside of Saddam's hometown, Tikrit, after capturing it, and killed a similar number of Yazidis and other religious minorities outside of Mosul, the north's biggest city.

Obama ordered air strikes in northern Iraq last month as Kurdish-controlled territory fell to the Islamic State and the capital of Iraqi Kurdistan looked in endangered.

Last weekend, U.S. warplanes carried out raids farther south in the province of Saluhuddin to break an Islamic State siege of the Shi'ite Turkmen town of Amerli.