Western countries are concentrating their diplomatic effort in Iraq's capital Baghdad, in a push to stop the Sunni insurgents called Islamic State.

France's Foreign Minister Laurent Fabius has urged that a "broad unity government" be forged in the country to combat the militants while on a visit to Baghdad, France 24 quoted him as saying.

Fabius stressed "all Iraqis should feel that they are represented" if the battle against terrorism is to be successful.

His trip came amid a third round of US air strikes against IS.

The latest developments followed information of mass murders of Yazidi (an ethno-religious minority) representatives, thousands of which are besieged by the extremists on Mount Sinjar.

UK officials say between 50 000 and 150 000 people are trapped there, facing starvation and dehydration, as the BBC reports. London, Washington, Paris and Baghdad are already delivering aid with planes to prevent the humanitarian crisis from further escalation.

According to an Iraqi minister, Islamic State reportedly killed over 500 Yazidis and threw them into a mass grave, a move that many media outlets described as "ethnic cleansing".

Human rights minister Mohammed Shia al-Sudani was quoted by Hurriyet Daily News as saying that some 300 women were kidnapped as slaves.

He argued IS buried alive some of the victims.

Thousands of Yazidis are reportedly fleeing to Turkey, with at least 1000 already waiting at Iraq's northern border with the country.

Turkey is not ready to open its frontiers despite their assurances there is a risk to their lives.

Ankara authorities have explained many of the asylum seekers do not have proper documents.

The Yezidi (also Yazidi), based mainly in Iraq, also populate certain parts of Armenia, Georgia, Syria, and Turkey.

Though speaking a Kurdish language, they adhere to a religion strongly influenced by Zoroastrianism, and are therefore considered by the Sunni extremists to be a creation of the "devil".

After Mount Sinjar was seized, some of the Yazidis captured were imposed a deadline until August 10 convert to Islam.

The Islamic State, on the other hand, has declared a "Caliphate" in the chunks of land it controls within both Iraq and neighboring Syria.

It is targeting Iraq's non-Muslim population in the territories it seizes, and thousands have sought to leave the country.

US President Barack Obama, who had earlier hinted air strikes might be an answer to the crisis, officially allowed them last week.

On Saturday he described the intervention as a "long-term project".

Prior to Fabius' visit, Washington had also tried to persuade Prime Minister Nouri al-Maliki that a national unity cabinet, including Sunni, Shia and Kurdish representatives, is needed to solve the crisis.