Wave of Iraqi Executions Feared in ISIS Takeover ISIS is known to behead people it deems unbelievers.

June 13, 2014 -- A top United Nations official warned today that the Islamic army that has taken over several Iraqi cities - and is known for beheading who it considers "unbelievers" - may have begun a massacre in the territory it now holds.

The Islamic militant force known as ISIS has rapidly overwhelmed the cities of Mosul, Tikrit, Baji and the towns through much of northern Iraq.

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U.N. Human Rights spokesman Rupert Colville said the agency has received reports that the militants carried out summary executions of civilians and Iraqi soldiers in Mosul. He cited a report of 17 civilians killed in just one street on Wednesday.

"The full extent of civilian casualties is not yet known, but reports received by ... the UN Mission in Iraq suggest that the number of people killed may run into the hundreds and the number of wounded is said to be approaching one thousand," Colville said.

Navi Pillay, the top United Nations human rights official, said today that she was "extremely alarmed" by reports of "summary executions and extrajudicial killings" in Mosul.

The militant group, whose initials stand for Islamic State of Iraq and the Levant, is composed of Sunni Muslims. The Iraqi government, its army and police are dominated by Shiite Muslims. Most of Iraq's armed forces fled before ISIS' approach. Human Rights Watch has documented a pattern of summary executions and torture in other areas of Syria and Iraq that it has conquered.

Reports from Syria over the past year document that ISIS often beheads those it executes.

"The possibility that ISIS will repeat the atrocities it has committed in other parts of Iraq, and impose the same intolerant and abusive rule as it has in Syria, is deeply troubling," said Nadim Houry, deputy Middle East director at Human Rights Watch.