GENEVA The United Nations human rights chief urged the Iraqi government and U.S.-led coalition on Tuesday to review tactics in Mosul to spare civilians he said were being deliberately put at risk by Islamic State. At least 307 civilians have been killed and 273 wounded in western Mosul between Feb. 17 and March 22 as Islamic State fighters herd people into booby-trapped buildings as human shields and fires on those who flee, according to U.N. figures. "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," U.N. High Commissioner for Human Rights Zeid Ra'ad al-Hussein said. "It is vital that the Iraqi Security Forces and their coalition partners avoid this trap," he said in a statement. "The conduct of air strikes on ISIL (Islamic State) locations in such an environment, particularly given the clear indications that ISIL is using large numbers of civilians as human shields at such locations, may potentially have a lethal and disproportionate impact on civilians," Zeid said. The rules of war, as set out in the Geneva Conventions, require respecting the principles of precaution, proportionality and distinguishing between combatants and civilians. Zeid also called on Iraqi and coalition forces to conduct transparent investigations into deadly incidents. Investigators are in Mosul to determine whether a U.S.-led coalition strike or Islamic State-rigged explosives caused a huge blast in al-Jadida district on March 17 that destroyed buildings, a U.S. military commander said. Official figures indicate that at least 61 people were killed in that incident, "but the actual figure may be much higher," Zeid's spokesman Rupert Colville told a news briefing. A municipal official had said on Saturday that 240 bodies had been pulled from the rubble. On March 22, an air strike hit a residential building in Rajm Hadid neighborhood. "ISIL reportedly filled the house with people from the surrounding neighborhood including children and then used the house to launch rocket-propelled grenades against the Iraqi security forces," he said, quoting survivors. "In terms of the air strikes that have caused casualties... that is also complicated by the fact that ISIL reportedly actually placed explosive devices in these same buildings which they had herded civilians into. So that will of course have compounded the devastation," Colville said. It is "essential the coalition and the Iraqi forces really try hard to minimize the impact on the civilians", he said. "Clearly not easy. We're not saying it is," Colville said. "But they do have obligations under international humanitarian law."