Islamic State advances against Yazidis on Iraq's Sinjar mountain

Displaced people from the minority Yazidi sect, who fled the violence from forces loyal to the Islamic State in Sinjar town, settle in abandoned houses as they take shelter in Mount Sinjar August 13, 2014. REUTERS/Rodi Said

ARBIL/BAGHDAD (Reuters) - Islamic State militants advanced on Iraq's Sinjar mountain on Tuesday, tightening a siege of thousands of stranded Yazidis, who called on the United States and its allies to act to avert more bloodshed.

The attack is the latest threat to minority Yazidis, thousands of whom have shot, buried alive or sold into slavery by IS militants, who regard them as devil-worshippers.