Islamic State fighters launched a series of attacks against Peshmerga positions across northern Iraq on Monday, the Iraqi Kurdish news agency Rudaw reported.

They included a truck bomb that killed 15 Peshmerga fighters near the Mosul Dam and a firefight that killed three close to the town of Qarah Tapah, the agency reported.

Leaders from the small Yazidi religious minority said the militants were conducting a fresh assault on the Sinjar mountain range in northern Iraq in a bid to reach and destroy the Sharaf Al Deen shrine, which is holy to Yazidis.

Qassim Hussein Burgez, a Yazidi leader and former Iraqi lawmaker, said volunteer forces were able to hold ground on the mountain range and repel an Islamic State attack that began early Monday from southern and western fronts. He said the militias would be hard-pressed to hold off further assaults without assistance from Iraq's military or nearby Kurdish forces.

"The situation could be disastrous," he said, adding that Yazidi fighters would soon run out of food and ammunition without support.

He estimated about 500 families remained on the mountain range, after most left in August during a heavy assault by Islamic State fighters that played a role in drawing U.S. intervention. An estimated 40,000 Yazidis fled the militant advance in August.

The U.S. military said it delivered meals and water to Yazidis trapped on the mountain and carried out airstrikes to stop Islamic State militants from closing in on the Kurdish city of Erbil or to allow local forces to aid the minority group.

Islamic State activists have boasted online of enslaving captured Yazidis--an ethnically Kurdish group that follows a pre-Islamic religion--whom they consider polytheists and apostates.

The U.S., France and the U.K. conducted six strikes in Iraq on Sunday and Monday, in coordination with Iraqi ground forces, U.S. Central Command said. The allied planes continued strikes in Anbar province and near Beiji, where Islamic State forces are in control of a key Iraqi oil refinery.

Three strikes south of the Beiji refinery destroyed or damaged a small Islamic State unit, two buildings and three vehicles, and one south of the city destroyed four boats and damaged at least four more, Central Command said.

The U.S. and partners struck a large Islamic State unit and three vehicles southeast of Fallujah, conducting two strikes there following an expansion of U.S. airstrikes in Iraq's Sunni-dominated Anbar province over the weekend. U.S. warplanes on Sunday struck a berm near the Fallujah Dam that Islamic State militants used to flood Shiite neighborhoods in East Fallujah.

Felicia Schwartz contributed to this article.

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