The UN's human rights chief expressed alarm on Friday at reports of extrajudicial killings and summary executions in Iraq as jihadists advance across the north, warning that civilians were particularly at risk.
"I am extremely concerned about the acute vulnerability of civilians caught in the cross-fire, or targeted in direct attacks by armed groups, or trapped in areas under the (militants') control," Navi Pillay said in a statement.
The rights chief said the situation in Iraq was deteriorating rapidly amid reports of "summary executions and extrajudicial killings and the massive displacement of an additional half a million people" by militants from the Islamic State of Iraq and the Levant (ISIL), the statement said.
In the past week, the fighters from the Islamist group have overrun a succession of major towns and cities and were moving closer to Baghdad on Friday.
According to the UN mission in Iraq, "the number of people killed in recent days may run into the hundreds and the number of wounded is said to be approaching one thousand," Pillay said.
She warned the parties to the conflict that they are obliged under international law to treat humanely members of the armed forces who have laid down their arms.
"Murder of all kinds, mutilation, cruel treatment and torture constitute war crimes," the statement said.
The UN had received disturbing reports after the capture of Iraq's second city Mosul, including the suicide of four women who had reportedly either been raped or forced to marry ISIL soldiers.
- Summary executions -
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Pillay also said she was deeply disturbed by reports that "ISIL fighters, including prisoners they had released from jails in Mosul and provided with arms, have been actively seeking out -- and in some cases killing -- soldiers, police and others, including civilians whom they perceive as being associated with the government."
One report included the "summary executions" of Iraqi army soldiers, as well as of 17 civilians, believed to have been working with the police, on one particular street in Mosul City on June 11.
Former prisoners had reportedly also gone "to Tikrit and killed seven former police officers who had worked in the prison," Pillay's spokesman Rupert Colville told reporters.
A court employee and 12 people believed to have been serving with Iraqi security services or police had been executed in the central Mosul neighbourhood of Dawasa, he added.
Militants have also carried out several kidnappings in Mosul, including the seizure of dozens of Turks from a consulate and 16 Georgians working for an Iraqi communications company.
"I am especially concerned about the risk to vulnerable groups, minorities, women and children," Pillay said, pointing to the group's "well-documented record of committing grave international crimes in Syria."
Many of the ISIL fighters, who split from Al-Qaeda last year, have been trained in arms and warfare in neighbouring Syria, where a special UN commission of inquiry concluded in March the group is committing "crimes against humanity".
Pillay said more efforts were needed to halt the movement of weapons and fighters across the Iraq-Syria border, stressing that the failure to stop the two conflicts from feeding each other had "predictably played a major role in the catastrophic situation affecting both countries today."
Pillay also called on the Iraqi government forces to show "utmost restraint" and to help protect civilians from violence as they battle the jihadists.
Even before ISIL's recent massive territorial gains, "violent terrorist acts" had killed 799 Iraqis and injured 1,409 others between January 1 and May 30 this year, according to the UN mission in Iraq.