Army General Joseph Votel, head of the US Central Command, told members of the House of Representatives on Wednesday that a probe into a recent bombing in the Iraqi city of Mosul has moved from an "assessment" to a formal investigation.

Speaking before members of the House Armed Services Committee, Votel said the investigation would seek to determine what role the US played in the civilian deaths in Iraq's second-largest city.

On March 17, an Iraqi military official said that an airstrike carried out by the US-led coalition struck an explosives-laden truck, killing dozens of non-combatants. The incident cast a new light on civilian casualties in the city, as the US and its regional allies seek to wrest control of it from the so-called "Islamic State" (IS) terrorist group. Iraqi forces regained control of the eastern part of Mosul in January, but much of the city still remains in the hands of IS, which first took over the city back in 2014.

Votel said IS is exploiting US sensitivities to civilian casualties and that the investigation would also look to determine what role the terror group played in the deaths, such as using civilians as human shields.

US airstrikes 'alarming': Amnesty

The general's announcement comes not long after both the UN and rights group Amnesty International expressed concern over the coalition's offensive in the city. On Tuesday, Amnesty released a report detailing the destruction that US-led airstrikes have left in their wake. "Evidence gathered on the ground in East Mosul points to an alarming pattern of US-led coalition airstrikes which have destroyed whole houses with entire families inside," Amnesty senior advisor Donatella Rovera said.

More than 3,000 civilians are believed to have died since US-backed government forces launched their onslaught into the city. Amnesty said the US is not taking adequate precautions to ensure the safety of non-combatants, though on Monday the US publically denied that it had loosened its rules of engagement on airstrikes against IS.

Additionally, Votel told members of the committee that 284 members of the Iraqi security forces had been killed since the fighting to retake Mosul began, adding that more than 1,600 had been wounded.

Also on Wednesday, Iraqi government forces edged closer to retaking a key area in western Mosul as they continue to battle with IS militants.

blc/jm (AP, Reuters)