Kurdish forces supported by US air strikes are battling to retake Mosul dam from Islamic State (IS) fighters in northern Iraq.
The operation to recapture the country’s largest dam began early on Saturday with raids by F-18 fighters and drones, US officials said.
Kurdish Peshmerga fighters have shelled militants’ positions, and there is an unconfirmed report of a ground attack.
Meanwhile, reports are coming in of new massacres by IS.
The extreme Sunni group, which overran Mosul this summer and seeks to build a new state spanning Iraq and Syria, has been accused of a new massacre of non-Muslims on Friday, in a village near Sinjar.
It was also accused on Saturday of recently killing 700 members of a tribe over the border, in Syria’s oil-rich Deir Ezzor province, in a report which could not be verified independently.
In another development, German Foreign Minister Frank-Walter Steinmeier visited Iraq, as Western states stepped up aid.
US Central Command said it carried out nine air strikes on Saturday, hitting targets near Irbil and Mosul dam.
The strikes “destroyed or damaged four armoured personnel carriers, seven armed vehicles, two Humvees and an armoured vehicle,” a statement said.
“All aircraft exited the strike areas safely.”
US military officials told NBC News the decision to try to retake the dam came after intelligence showed IS militants “were not yet at a point where they could blow up the installation”.
A Kurdish commander, Major General Abdelrahman Korini, told AFP that the Peshmerga had captured the eastern side of the dam and were “still advancing”.
Rudaw, a Kurdish news website, said the air strikes appeared to be the “heaviest US bombing of militant positions since the start of air strikes” against IS last week.
At least 11 IS fighters were killed by the air strikes, sources in Mosul told BBC News.
The dam, captured by IS on 7 August, is of huge strategic significance in terms of water and power resources.
Located on the River Tigris about 50km (30 miles) upstream from the city of Mosul, it controls the water and power supply to a large surrounding area in northern Iraq.
The BBC’s Jim Muir in Irbil says there are fears the dam is structurally dubious and many have warned that it could unleash a catastrophic flood if it was breached.
At least 80 men from the Yazidi faith were killed, and scores of women and children abducted, in the village of Kawju (also spelt Kocho) on Friday afternoon, Kurdish and Yazidi sources say.
Reports say the men were killed after refusing to convert to Islam. A US drone strike later destroyed two vehicles belonging to the militants.
A Yazidi refugee from a different village, Moujamma Jazira, told AFP news agency that people there had tried in vain to fight back but were outgunned.
Dakhil Atto Solo said that 300 men had been executed by IS in Moujamma Jazira, and the women and children abducted. The report could not be verified independently.
Meanwhile, UK-based Syrian opposition activists reported that IS had executed 700 members of the al-Sheitaat tribe in Deir Ezzor.
“Reliable sources” reported that many of the tribesmen had been beheaded, the Syrian Observatory for Human Rights said.
Tribesmen in the area had tried to drive out IS at the beginning of the month, in a rare display of local resistance. IS rushed in reinforcements in response.
The group first emerged during Syria’s bloody three-year civil war.
Visiting Baghdad, Germany’s foreign minister met the new Prime Minister, Haider al-Abadi, who took over from Nouri Maliki this week.
He said he hoped Mr Abadi would be able to represent all the different regions and religions in the country, as this was the only way to prevent disenchanted Iraqis from backing IS.
German military transport planes have already begun delivering aid through the Kurdish city of Irbil but Germany is legally prevented from arming countries involved in conflict.
Two Airbus flights carrying UK aid supplies arrived in Irbil on Saturday.
On a stop in the city, Mr Steinmeier met Yazidi refugees.
IS-led violence has driven an estimated 1.2 million Iraqis from their homes. Whole communities of Yazidis and Christians have been forced to flee in the north, along with Shia Iraqis, whom IS do not regard as true Muslims.