ISIS has "executed" 232 people near the Iraqi city of Mosul and taken tens of thousands of people to use as human shields against advancing Iraqi forces, the United Nations says.

The terror group carried out the mass killings Wednesday, punishing people who had defied its orders, a spokeswoman for the UN human rights arm told CNN.

"ISIS executed 42 civilians in Hammam al-Alil, south of Mosul. Also on Wednesday ISIS executed 190 former Iraqi security forces for refusing to join them, in the Al Ghazlani base near Mosul," said Ravina Shamdasani of the Office of the UN High Commissioner for Human Rights.

Another 24 former Iraqi security forces officers were reportedly killed Tuesday, the office said.

Since October 17, ISIS has taken tens of thousands of men, women and children from the outskirts of Mosul into the city. Shamdasani said the United Nations feared the group intended "to use them as human shields against the Iraqi forces advance on Mosul."

There have been other reported civilian deaths over the past week as ISIS tries to herd people into its last major stronghold in Iraq and the nation's second city against the Iraqi-led operation.

(CNN)