BAGHDAD: Islamic State militants have killed at least 500 members of Iraq's Yazidi minority in northern Iraq, burying some of their victims alive and kidnapping hundreds of women, a Baghdad government minister said on Sunday.

The insurgents' advance through northern Iraq has forced tens of thousands to flee, threatened the capital of the Kurdish autonomous region and provoked the first US air strikes in the area since Washington withdrew troops from Iraq in 2011.

Iraq's human rights minister Mohammed Shia al-Sudani told Reuters that he had evidence that the Sunni militants had thrown the Yazidi dead into mass graves, adding that some of those buried alive were women and children. About 300 women had been forced into slavery, he said.

President Barack Obama said on Saturday that US air strikes had destroyed arms that the Islamic State, which has captured swaths of northern Iraq since June, could have used against the Iraqi Kurds, but he warned that there was no quick fix for the crisis that threatens to tear Iraq apart.

US military aircraft have also dropped relief supplies to tens of thousands of Yazidis who have collected on the desert top of Mount Sinjar seeking shelter from the insurgents, who had ordered them to convert to Islam by Sunday or die.

Sudani said news of killings had come from people who had escaped from nearby Sinjar, the ancient home of the Yazidis and one of the towns captured by the Sunni militants who view the community as “devil worshipers”.

“We have striking evidence obtained from Yazidis fleeing Sinjar and some who escaped death, and also crime scene images that show indisputably that the gangs of the Islamic States have executed at least 500 Yazidis after seizing Sinjar,” Sudani said. “Some of the victims, including women and children were buried alive in scattered mass graves in and around Sinjar.”

Speaking before US warplanes struck militant targets for the second straight day, Obama said it would take more than bombs to restore stability, and criticised Prime Minister Nuri al-Maliki's Shia-led government for failing to empower Iraq's Sunnis.

France joined the calls for Iraq's feuding leaders to form an inclusive government capable of countering the militants. “Iraq is in need of a broad unity government, and all Iraqis should feel that they are represented in this government,” Foreign Minister Laurent Fabius said.

“All Iraqis should feel they are represented to take part in this battle against terrorism,” he told a news conference with his Iraqi counterpart in Baghdad in comments translated into Arabic on state television. Maliki's critics say his sectarian agenda prompted heavily-armed Sunni tribes to join the insurgency.

But Maliki, serving in a caretaker capacity since an inconclusive election in April, has defied calls by Sunnis, Kurds, fellow Shias, regional power broker Iran and Iraq's top cleric to step aside for a less divisive leader.

Wake up call

The pressure from France came a day after Obama described the upheaval in the north as a “wake up call” to Iraqis who have slipped back into sectarian bloodshed not seen since a civil war peaked in 2006-2007.

Nearly every day police report kidnappings, bombings and execution-style killings in many cities, towns and villages. The Islamic State, which sees Shias as infidels who deserve to be killed, has met little resistance.

Thousands of US-trained Iraqi soldiers fled when its Arab and foreign fighters swept through northern Iraq from eastern Syria in June.

The collapse of the Iraqi army prompted Kurds and Shi'ite militias to step in, with limited success.

The Sunni militants routed Kurds in their latest advance with tanks, artillery, mortars and vehicles seized from fleeing soldiers, calling into question their reputation as fearsome “those who confront death” warriors.

Iranian-trained Shia militias may stand a better chance than the Kurds but they are accused of kidnapping and killing Sunnis, playing into the hands of the Islamic State, which also controls a large chunk of western Iraq.

After hammering Kurdish forces last week, the militants are just 30 minutes' drive from Arbil, the Iraqi Kurdish capital, which until now has been spared the sectarian bloodshed that has scarred other parts of Iraq for a decade.

The possibility of an attack on Arbil has prompted foreigners working for oil companies to leave the city and Kurds to stock up on AK-47 assault rifles at the arms bazaar.

In their latest sweep through the north, the Sunni insurgents routed Kurdish forces and seized a fifth oil field, several more villages and the biggest dam in Iraq - which could give them the ability to flood cities or cut off water and power supplies - hoisting their black flags up along the way.

After spending more than $2 trillion on its war in Iraq and losing thousands of soldiers, the United States must now find ways to tackle a group that is even more hardline than al-Qaeda and has threatened to march on Baghdad.

Iraqi security and intelligence officials told Reuters Islamic State fighters based in the western cities of Falluja and Ramadi have been using tunnels built by former dictator Saddam Hussein in the 1990s to evade UN weapons inspectors to sneak across to towns just south of the capital.