The US has launched five air attacks on Islamic State fighters threatening the Haditha dam, as Washington widened its air campaign against the group.
The attacks on Sunday destroyed Islamic State vehicles, two of which were carrying anti-aircraft artillery, a fighting position and a command post, the US central command said.
"At the request of the Iraqi government and in keeping with our mission to protect US personnel and facilities, US military planes have begun striking ISIL terrorists near the Haditha dam," said a US official.
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Al Jazeera's Jane Arraf, reporting from Baghdad, said the bombardment targeted IS fighters between Haditha and al-Qaim, close to the Syrian border.
"That area is key to defeating or at least containing IS who use the route to transport weapons," she said.
Iraqi helicopters were also taking part in the offensive, the Iraqi defence ministry said.
Iraqi state television said government troops had taken control of the northern entrance of the town of Berwana, about 15km south of Haditha and that 15 IS fighters were killed.
Last month, IS fighters tried to capture the Haditha dam, which has six power generators alongside the country's second-largest reservoir. Iraqi forces backed up by local Sunni tribes were able to hold them off.
The IS group was able to take control of the Mosul dam in northern Iraq last month, but US air strikes helped Kurdish and Iraqi forces to retake it.
An interior ministry spokesman told Al Jazeera that US support was crucial to beating the Islamic State group.
"If we want a remedy for this cancer... help from the American side will tackle it in a shorter time - especially when we are talking about air power," he said.
In a separate development, Kurdish peshmerga fighters supported by the Iraqi air force have retaken Gazzer mountain, close to Kalak on the road to Mosul, sources told Al Jazeera.
Peshmerga forces are advancing from the east and west on Mosul, the stronghold of the Islamic State group in Iraq.
The attacks came as the Arab League promised to take all necessary measures to combat the Islamic State group.
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"What is needed is a clear decision for a comprehensive confrontation, militarily and politically," Arab League chief Nabil el-Araby said on Sunday.
The Arab League also endorsed a UN Security Council resolution passed last month calling on member states to "act to suppress the flow of foreign fighters, financing and other support to Islamist extremist groups in Iraq and Syria".
The US president, Barack Obama, last week announced a Nato-led "core coalition" to confront the group in Iraq and Syria, and called on Arab states to consider military action.
Source: Al Jazeera and agencies