The US has carried out a new round of air strikes against Islamic State militants in northern Iraq as pressure mounts on MPs to be recalled to Parliament to debate the crisis.

Islamic State militants have now killed hundreds of Christians from Iraq's minority Yazidis, burying some alive and taking women as slaves, Iraqi officials said, as US warplanes again bombed the insurgents yesterday.

The country's human rights minister Mohammed Shia al-Sudani accused the Sunni Muslim insurgents, who have ordered the community they regard as "devil worshippers" to convert to Islam or die, of celebrating a "a vicious atrocity" with cheers and weapons waved in the air. No independent confirmation was available.

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US drone aircraft and fighter jets had hit armed trucks and mortar positions near Arbil, the capital of the autonomous Kurdish region which had been relatively stable throughout Iraq's years of turmoil until the insurgents swept across the north.

RAF aircraft over the weekend dropped bundles that included 1200 reusable water containers, providing 6000 litres in total and 240 solar lanterns that can also be used to recharge mobile phones.

The UK's humanitarian effort aimed to helped the trapped Yazidi people on Mount Sinjar and will be stepped up over the coming days.

Britain is also planning to send more advisers to the town of Irbil, which is under threat from extremists.

The former chief of the General Staff, Lord Dannatt, said MPs should be recalled from their summer holidays to debate the crisis in the Commons.

He said that Britain was "watching in horror" as atrocities were committed.

Writing in a Sunday newspaper, Lord Dannatt wrote: "In the face of a crisis of this scale, with the potential for so much human misery, this is not the moment for decision-makers to be on holiday. Parliament needs to be recalled and the West needs to face up to its responsibilities."

After a meeting of the Government's Cobra emergency committee, a Number 10 spokesman said: "The humanitarian situation remains deeply worrying and consequently this continues to be our priority.

"Hundreds of thousands of people are displaced across the region and in need of aid supplies. And thousands are still trapped on Mount Sinjar, although it is understood that some may have escaped off the mountain to the north.

Meanwhile, President Barack Obama's bombing raids have come under fire for being ineffective.

New York Republican congressman Peter King criticised his insistence he will not send ground troops to combat the militants, adding the US has been too timid so far.

"We should take nothing off the table. We (should) start off with massive air attacks," Mr King, a member of the House of Representatives Homeland Security Committee said.

"I think doing them from aircraft carriers is limiting them. We should use bases in the area so we can have much more sustained air attacks. We should be aggressively arming the Kurds," King added.

Last week, Mr Obama launched a campaign of US air strikes and humanitarian air drops in areas where militants, who have seized large swathes of Iraq since June, are threatening religious minorities and encroaching on Arbil, the capital of Iraq's autonomous Kurdish region. The moves are the first direct US military action in Iraq since Mr Obama pulled troops out in 2011.

Mr Obama, who campaigned on ending the country's involvement in the long and bloody conflict, is reluctant to wade back into Iraq.

The President stressed the overall solution for the country rests with Iraqi political leaders.