It will take a while to find out what exactly happened in the town of Sinjar in northern Iraq. But already the discovery of six mass graves, some of them booby-trapped with bombs, has thrown attention back on to the terrible crimes inflicted on the Yazidi population by so-called Islamic State (IS).
One of the graves contains the bodies of about 80 women thought to be too old to serve as sex slaves.
Now there's growing speculation that the US may soon start calling these and other crimes against the Yazidis genocide. There have also been calls in the UK for Prime Minister David Cameron to use the term to describe the killing of minorities by IS.
The term genocide was coined by Raphael Lemkin, a Jewish lawyer who escaped from Poland, towards the end of World War Two. It consists of the Greek genos, meaning race, and the Latin cide, meaning killing.
A UN declaration in 1948 defined it as "acts committed with the intent to destroy, in whole or in part, a national, ethnic, racial or religious group".
A recent report by the US Holocaust Memorial Museum argued this is exactly what IS is doing to the Yazidis. It cited eyewitness accounts of how IS has captured the Iraqi village of Kocho in August 2014, executing Yazidi men and enslaving Yazidi women out of a belief they are devil-worshippers.
But, controversially, the report stopped short of calling the treatment of Christians or other minorities genocide arguing that IS at least gave them the option of avoiding death by paying taxes or converting.
Loaded term
Using a word which describes the ultimate crime is a big move for a country like the US. It was last deployed by Colin Powell, when he was Secretary of State, to describe the killings in Darfur in 2004.
But historically there have been many rows about what actually constitutes genocide and how much evidence is needed to prove a clear intent to exterminate a particular group.
Witness, for example, the fierce ongoing debate about whether the mass killings of Armenians by the Ottoman Turks in 1915 amounted to genocide. Governments can also be reluctant to use the term if they think they might be required to wade into a conflict and stop it.
The US avoided using the word during the fighting in Rwanda in 1994 that saw 800,000 people, mostly Tutsis, slaughtered. A State Department memo later revealed its lawyers were worried: "Be Careful... Genocide finding could commit USG (United States Government) to 'do something'."
The Rwandan genocide took place over a period of approximately 100 days from April to July 1994
In the case of IS, however, the US would argue it is already doing something by conducting air strikes, so that might actually embolden Mr Obama to start using the G-word soon.
'The word matters'
For the Yazidi community, it would be a moment of huge symbolism if the US does adopt the term.
But there could be practical implications too. If the UN Security Council voted to refer the issue to the International Criminal Court (ICC), an official case would be opened, evidence gathered and potentially individuals indicted at The Hague.
None of this, of course, would happen quickly. But Pari Ibrahim, a Yazidi activist, is adamant that "the word genocide matters".
"Starting an ICC case will eventually bring recognition, reparations and ensure the protection of civilians in the future," she says.
One hundred and fifty-eight members of Congress have now signed a motion calling for the US to start using the word to describe the worst crimes of IS.
Many believe a change in language would stiffen political resolve in the broader fight against IS.
They argue other phrases such as "ethnic cleansing" or "crimes against humanity" have less impact.
'Differentiating suffering'
But Prof Philippe Sands, an expert in international law, believes the word genocide can sometimes be problematic because it risks creating a hierarchy of IS's victims, saying: "Its use elevates the suffering of one group and might unwittingly diminish the crimes against other groups by suggesting their suffering is somehow less significant."
Already the White House is discovering that language is tricky. The State Department is being lobbied by Catholic bishops (including the Cardinal Archbishop of Washington) who fear the term might be applied only to the Yazidis and not to Christians and other minorities who have also suffered at the hands of the self-declared caliphate.
They reject the idea that IS offers Christians preferential treatment compared to the Yazidis and they point to the fact that Pope Francis himself has already used the word genocide to describe their plight.
Yet even if the US did include the Christians, there would be others – the Kurds or the Turkmen, for example – who could in turn argue that they were being excluded.
Using the G-word would help President Obama ramp up the international rhetoric against IS in 2016 and would throw more light on their terrible crimes.
But such is the potency of this strictly defined word that it might also cause the White House some political headaches if other minorities feel they are being forgotten.
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1948 UN declaration
In the present convention, genocide means any of the following acts committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such:
- killing members of the group
- causing serious bodily or mental harm to members of the group
- deliberately inflicting on the group conditions of life calculated to bring about its physical destruction in whole or in part
- imposing measures intended to prevent births within the group
- forcibly transferring children of the group to another group