Muslim groups and leaders from across the world, including those from the US, have strongly condemned the barbarism unleashed by the Islamic State, also known as Islamic State of Iraq and Syria or ISIS, describing the extremist outfit's behaviour as "un-Islamic".

"We strongly condemn this gruesome and barbaric killing as a violation of Islamic beliefs and of universally-accepted international norms mandating the protection of prisoners and journalists during conflicts," said the Council on American-Islamic Relations (CAIR), the nation's largest Muslim civil rights and advocacy organization.

CAIR's remarks came days after the ISIS released a video showing one of its members beheading American journalist James Foley, who was abducted in Syria in November 2012.

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