Islamic State has been carrying out mass killings in Mosul amid a government-led offensive to retake the city, according to reports made to the UN human rights office.
Spokeswoman Ravina Shamdasani said the office has received reports of an incident in which IS allegedly killed 50 of its own militants at the Ghazlani military base in Mosul "for alleged desertion".
Ms Shamdasani also told reporters that her office has had reports indicating four women were killed and 17 other civilians wounded in air strikes on Wednesday in the Quds neighbourhood of eastern Mosul.
She also cited reports that IS has been holding nearly 400 women captive in the nearby town of Tal Afar.
The updates came as heavy fighting erupted in eastern neighbourhoods of Mosul as Iraqi special forces launched an assault deeper into urban areas of the city and swung round to attack IS militants from a second entry point in the north east.
Columns of armoured vehicles wound through open desert to open the new front, pushing through dirt embankments, drawing heavy fire and calling in air strikes to enter the middle class neighbourhoods of Tahrir and Zahara. The area was once named after former Iraqi dictator Saddam Hussein.
Lieutenant Colonel Muhanad al-Timimi said three militants in separate explosives-laden vehicles tried to attack the troops but they were destroyed, including a bulldozer that was hit by an air strike from the US-led coalition supporting the offensive.
At least one solider was seriously wounded in the first hours of the new advance, which came under heavy fire from mortars, automatic weapons, snipers and anti-tank rockets. Commanders at the scene said his neck injury could have been the result of small arms fire or shrapnel from a mortar round.
Earlier, at the direct eastern approach to the city's urban centre, militants holed up in a building fired a rocket at an Abrams tank, disabling it and sending its crew fleeing from the smoking vehicle, seemingly unharmed. The advance in that area then stalled.
The day's fighting has been the most intense urban combat in Mosul since the Iraqi offensive began over two weeks ago to drive IS from Iraq's second-largest city.
The early morning push began with artillery and mortar strikes on the Aden, Tahrir and Quds districts, just west of special forces footholds in the Gogjali and Karama neighbourhoods, Lt Col al-Timimi said. Both sides opened up with small arms and mortar fire after an artillery barrage by special forces, ahead of their advance.
IS is fighting to hold Mosul as Iraqi forces and allied Kurdish troops squeeze in from all directions with US-led coalition support, mostly from air strikes and reconnaissance.
On Tuesday, Iraqi troops entered the city limits for the first time in more than two years. Soldiers had withdrawn from Mosul in 2014 in the face of an IS blitz that seized large areas of territory in Iraq and neighbouring Syria.
Now the Iraqi forces are gearing up for urban warfare expected to take weeks, if not months, as they work their way neighbourhood by neighbourhood, going through a warren of dense buildings prone to booby traps and ambushes.
More than a million civilians are stuck in the city, complicating the military's efforts to advance without harming innocents.
IS militants have driven thousands of them deeper into the city's built-up areas, apparently for use as human shields, while hundreds of others have fled in recent days towards government-controlled territory despite the uncertainty of resettlement in displacement camps.
Mosul is the last major IS stronghold in Iraq, and expelling the militant group from it would be a major blow to the survival of its self-declared "caliphate" that stretches into Syria. When IS seized Mosul and other territory in 2014, the much larger Iraqi military had been neglected and demoralised by corruption.
Iraqi forces have made uneven progress in closing in on the city since the operation began on October 17. Advances have been slower to the south, with government troops still 20 miles away, although they seized a handful of villages late last week.
Kurdish fighters and Iraqi army units are deployed to the north, while government-sanctioned Shiite militias are sweeping in from the west to try to cut off any IS escape route.
One of the leading Shiite militias, the Hezbollah Brigades, said on Wednesday that its fighters had gained control of a highway linking Mosul to the Syrian city of Raqqa, the de facto capital of the militants' self-proclaimed caliphate.
The militias' umbrella group, the Popular Mobilisation Units, say they will not enter Mosul and will instead focus on retaking Tal Afar, a town to the west that had a Shiite majority before it fell to IS in 2014.