A 15-year-old Yazidi girl captured by the Islamic State group after escaping. (Associated Press)

The campaign of Islamic State militants against Iraq's Yazidi minority may be attempted genocide, UN Assistant Secretary-General for human rights Ivan Simonovic said on Tuesday."Facts are indicating that actions against Yazidis may amount to attempted genocide," he told a small group of reporters at the United Nations after returning from a recent visit to Iraq.Simonovic was speaking as Islamic State, often referred to as ISIL or ISIS, advanced on Iraq's Sinjar mountain, tightening a siege of thousands of stranded Yazidis, who called on the United States and its allies to act to avert more bloodshed.Thousands of Yazidis have been shot, buried alive or sold into slavery by Islamic State militants, who regard them as devil-worshippers.US President Barack Obama authorised air strikes in Iraq in August, citing the duty to prevent an impending genocide of Yazidis at the hands of Islamic State militants after they overran a vast swathe of northern Iraq.The 1948 UN Convention on the Prevention and Punishment of the Crime of Genocide defines genocide as an intent to destroy in whole or in part a national, ethical, racial or religious group.The convention says this can be done by killing members, causing serious bodily or mental harm to members, deliberately inflicting conditions on the group calculated to bring about its physical destruction, preventing births within the group or forcibly transferring children of the group to another group.

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Simonovic said that Islamic State was forcing Yazidis to either convert to Islam or be killed with the intent of destroying the religious group.Islamic State originally attacked the area around Sinjar, in northwestern Iraq, in August. A renewed assault began at dawn on Monday, when militants driving Humvees and civilian vehicles attacked several Yazidi residential compounds, forcing the Yazidis to retreat up the mountain.