As Iraq forces inch towards the outskirts of Mosul, the UN said Tuesday (October 25th) it had received reports of dozens of execution-type killings by the "Islamic State of Iraq and the Levant" (ISIL) , including the slaying of 50 former police officers, AFP reported.

The allegations -- which remain "preliminary" -- have come from a range of civilian and government sources, who cannot be named for security reasons, said UN rights office spokesman Rupert Colville.

The reported atrocities were perpetrated by ISIL between Wednesday and Sunday, while Iraqi forces advanced towards Mosul, Colville said.

In a village called Safina, about 45 kilometres south of Mosul, ISIL was blamed for executing 15 civilians before throwing their bodies in a river, possibly to strike terror among other residents.

On October 19th also in Safina, extremist fighters "reportedly tied six civilians to a vehicle by their hands and dragged them around the village, apparently simply because they were related to a particular tribal leader fighting against ISIL", Colville said.

Iraqi security forces found another 70 bodies riddled with bullet wounds on October 20th in the nearby Tuloul Naser village. Colville said it was not immediately clear who was responsible for their deaths.

And on Saturday, ISIL gunmen allegedly shot dead three women and three girls during a forced march in Rufeila village south of Mosul.

The group was killed because they were struggling to keep up, likely because one of the girls who was ultimately shot dead had a physical disability, the rights office said.

The 50 police officers who had been held hostage by ISIL were reportedly executed in a building outside Mosul on Sunday, Colville told reporters in Geneva.

"We very much fear that these will not be the last such reports we receive of such barbaric acts by ISIL," he said, adding that all the allegations "need a bit more (investigative) work" before the UN can conclusively say they took place.

UN planning for 150,000 displaced

Meanwhile, Iraqi forces were inching to within striking distance of eastern Mosul Tuesday.

Forces from the elite counter-terrorism agency retook four villages close to the north-eastern outskirts of Mosul, their commander, Gen. Abdelghani al-Assadi, told Diyaruna.

"The Iraqi flag was raised on Teba, Toub Zawa, al-Mwafaqiya and Tahrawa villages," he said.

"We must now co-ordinate with forces on other fronts to launch a co-ordinated" attack on Mosul, he told AFP.

The UN refugee agency is preparing to receive 150,000 Iraqis fleeing the fighting in Mosul, its chief said Monday.

" The preparations are proceeding well ... UNHCR is going to have in two or three days 30,000 tents in Iraq, enough for 150,000 people," Filippo Grandi told reporters in Jordan after visiting Iraq.

A million people could be displaced, sparking an unprecedented humanitarian emergency in a country where the UNHCR says more than three million people have already been forced from their homes since the start of 2014.

Grandi said a key issue was "to find enough sites to be able to receive this huge mass of people should it come out of Mosul".

"Negotiations in this respect are going on with the government of Iraq and with the Kurdish regional government," he said.

So far, "the outflow of displaced people is not yet from the city of Mosul but from the outskirts" where there has been fighting, Grandi said.

"We have about 7,500 displaced people that have moved from the outskirts of Mosul to other locations that have been assisted and we have perhaps around 1,000 that have crossed into Syria," he said.