At least 307 civilians have been killed and 273 wounded in western Mosul since February 17 as fighters in the Islamic State group herd people into booby-trapped buildings as human shields and fires on those who flee, the United Nations human rights chief said on Tuesday.

“This is an enemy that ruthlessly exploits civilians to serve its own ends, and clearly has not even the faintest qualm about deliberately placing them in danger," UN High Commissioner for Human Rights Zeid Ra'ad al-Hussein said in a statement.

"It is vital that the Iraqi Security Forces and their Coalition partners avoid this trap," he said, while calling for them to conduct transparent investigations into deadly incidents involving their forces.

Even as the new figures emerged, the New York Times quoted U.S. military officials as saying that 240 additional troops would deploy to Iraq in the next 36 hours to help in the final push to retake Mosul.

According to the report, the troops, from the 82 Airborne Division, are not expected to serve in front-line combat but will be in dangerous areas and will include one platoon with equipment to clear away roadside bombs.

Investigators on the ground

Funerals in Mosul after coalition airstrikes.

Investigators are in the Iraqi city of Mosul to determine whether a U.S.-led coalition strike or Islamic State-rigged explosives caused a huge blast that destroyed buildings and killed more than 200 people, a U.S. military commander said.

Conflicting accounts have emerged since the March 17 explosion in al-Jadida district in west Mosul, where Iraqi forces backed by U.S.-led coalition air strikes are fighting to clear Islamic State militants from Iraq's second city.

Iraq's military command has blamed militants for rigging a building with explosives to cause civilian casualties, but some witnesses say it was collapsed by an air strike, burying many families under the rubble.

If confirmed, the toll would be one of the worst since the 2003 U.S.-led invasion, raising questions about civilian safety as Iraq's Shi'ite-led government tries to avoid alienating Mosul's mostly Sunni population.

U.S. Army chief of staff Gen. Mark Milley, after meeting Iraqi Prime Minister Haider al-Abadi and Iraq's defense minister late on Monday, said there had been airstrikes in the vicinity that day and on previous days, but it was not clear they had caused the casualties.

Open gallery view Displaced residents who fled their homes move to be searched by Iraqi troops, in western Mosul, Iraq March 28, 2017. Credit: SUHAIB SALEM/REUTERS

"It is very possible that Daesh blew up that building to blame it on the coalition in order to cause a delay in the offensive on Mosul and cause a delay in the use of coalition air strikes," Milley said, using an Arabic term for Islamic State.

"It is possible that a coalition air strike did it. We don't know yet. There are investigators on the ground."

A senior Russian general has criticized the coalition fighting ISIS for allegedly targeting infrastructure — including a key dam — in territory held by the extremist group in Syria.

Col. Gen. Sergei Rudskoi of the military's General Staff on Tuesday accused the coalition of trying to "completely destroy critical infrastructure in Syria and complicate post-war reconstruction as much as possible."

Rudskoi said that the collapse of the dam would cause an "ecological catastrophe" and lead to "numerous" civilian deaths. The U.S.-led coalition says it's taking every precaution and that the dam hasn't been structurally damaged.

A source close to Abadi's office said the U.S. military delegation also called for more coordination among the Iraqi security force units on the ground and for consideration that thousands of civilians are stuck in their homes.

Not enough precautions

Iraqi forces advance further into Mosul's Old City

Iraqi forces have retaken eastern Mosul and are pushing through the west but have faced tough resistance in the densely populated districts around the Old City, where narrow streets and traditional homes force close-quarters fighting.

Iraqi forces fighting around the Old City tried to storm the al-Midan and Suq al Sha'areen districts, where Islamic State ran its religious police who carried out brutal punishments, such as crucifixion and public floggings, federal police commander Lt. Gen. Raed Shakir Jawdat told state al-Sabah newspaper.

The battle is focused now on the Old City where troops are moving on the Al Nuri mosque, where Islamic State's leader declared his caliphate nearly three years ago after militants took control of swaths of Iraq and Syria.

Thousands of civilians are fleeing the fighting, shelling and air strikes, but as many as half a million people may be trapped inside the city. Fleeing residents say they have been used as human shields by militants who shelter in their homes.

The Iraqi Observatory for Human Rights said since the campaign against western Mosul began on February 19, unconfirmed reports have said nearly 700 civilians have been killed by government and coalition air strikes or Islamic State action.

Rights Group Amnesty International said on Tuesday the high civilian toll suggested U.S.-led coalition forces leading the offensive in Mosul failed to take adequate precautions to prevent civilian deaths.

"The fact that Iraqi authorities repeatedly advised civilians to remain at home instead of fleeing the area, indicates that coalition forces should have known that these strikes were likely to result in a significant numbers of civilian casualties," said Amnesty's Donatella Rovera, who carried out field investigations in Mosul.

The al-Jadida incident is far from clear. Witnesses on Sunday described horrific scenes of body parts strewn over rubble, residents trying desperately to pull out survivors and other people buried out of reach.

The Iraqi military's figure of 61 bodies was much lower than that given by local officials - a municipal official had said on Saturday that 240 bodies had been pulled from the rubble. A local lawmaker and two witnesses say a coalition air strike may have targeted a truck bomb, triggering a blast that collapsed buildings.