They sit on a mountaintop, trapped without food or water; followers of a mysterious ancient faith, surrounded by Islamic militants who now threaten to kill them all.

On the other side of the world, a US president has declared he is prepared to wade back into the Iraq quagmire by launching airstrikes to protect them.

So who are the Yazidis?

The Yazidis are a Kurdish-speaking religious/ethnic minority who have maintained their faith despite centuries of persecution.

Yazidis are secretive about their complex religion, its rituals, and its origins, and this has often led to misunderstandings and fuelled tensions.

Their faith is believed to have been derived in part from ancient Persian Zoroastrianism, which pre-dates both Islam and Christianity, although some modern scholars dispute this Zoroastrian link.

Yazidi spirituality and practices also include elements and traditions of Christianity, Islam and the Judaism. Adherents believe they were created separately from the rest of mankind and are descended from Adam, but not Eve.

The peacock people

The Yazidi people are defined by their monotheistic faith, with a belief in one Supreme Being, Yazdan, from whom seven great spirits emanate.

The paramount spirit is the Peacock Angel, who carries out Yazdan’s divine wishes. Yazdan and the Peacock Angel are regarded as inseparable.

This is an oral culture, with the traditions and secrets passed down through the generations.

In traditional Yazidi society a Chief Sheikh fulfils the role of supreme religious leader, while a secular emir rules a community structured under a rigid caste system.

Displaced families from the minority Yazidi sect walk on the outskirts of Sinjar. ( Reuters )

Conversion to the faith is prohibited, as is marriage to non-Yazidi, and unions between different castes is also banned.

In recent years, there have been reports of honour killings of Yazidi women who attempted to marry outside their faith.

In 2007, the stoning to death of a 17-year-old Iraqi-Yazadi girl received global attention.

At the core of this rigid, uncompromising social structure is a fundamental Yazidi belief in purification of the soul through a continuous process of rebirth.

Adherents believe that leaving the community and the faith is catastrophic – as the life cycle is broken and spiritual purity can never be achieved.

Accused of devil worship

Relations between Yazidis and their majority Muslim-Kurd neighbours have often been tense. According to Kurdwatch: "Many Muslims consider the Malak Taus (Peacock Angel) - the highest of the seven angels who rule the world and a key figure of the Yazidi faith – to be the personification of the devil. Accordingly the Yazidi are seen as 'devil worshippers'."

Some Muslims – including Sunni insurgents of the Islamic State (IS), formerly the Islamic State of Iraq and Syria (ISIS), believe the Yazidi are "apostates" or Muslims who have renounced their faith, an offence that in its extremist IS interpretation is punishable by death.

Historically the Yazidi lived in communities across northern Iraq, Syria and Turkey, with smaller numbers in Georgia and Armenia.

During the centuries of Ottoman rule, periodic purges forced many Yazidi communities to flee their traditional homelands and seek refuge elsewhere.

In the early 21st century, the age-old persecutions have continued. During the US led occupation of Iraq, the Yazidi were targeted in a campaign of insurgent bombings.

Sorry, this video has expired Thousands of Yazidis flee to Iraqi mountains to escape violence

The deadliest came in August 2007 when four coordinated suicide attacks claimed more than 500 lives in two Yazidi towns near Mosul.

Estimates on the size of the modern Yazidi community and diaspora vary wildly, ranging from 70,000 to 500,000, with the largest concentration in the northern Iraq province of Nineveh.

Smaller communities lived across northern Syria, although their fate since the start of the Syrian civil war remains unclear.

Large numbers emigrated to Germany and about 4,000 reportedly now live in Sweden.

Last Sunday fighters of the Islamic State (IS) publicly proclaimed the Yazidi to be "devil worshippers" as they seized the Iraqi town of Sinjar, the ancestral home of the Yazidi.

After occupying Sinjar and immediately blowing up a Shia Muslim shrine in the town, IS fighters declared that all residents convert to their interpretation of Sunni Islam, or face execution.

This demand triggered a mass exodus of tens of thousands of residents, both Yazidi and Iraqi Christians, who fled in vehicles and on foot, many striking out to the nearby mountain in the desperate misguided centuries-old belief that the heights would afford at least temporary respite from persecution.