US military opens investigation into Mosul airstrike General Joseph Votel says rules of engagement have not changed.

 -- The U.S. military is now conducting a formal investigation into what role a U.S. airstrike may have played in the deaths of as many as 200 civilians in Mosul, Iraq.

General Joseph Votel, the commander of U.S. Central Command, told a congressional committee that there has been no change in the rules of engagement regarding airstrikes targeting ISIS in Iraq and Mosul.

The U.S.-led coalition fighting ISIS has acknowledged that a March 17 airstrike in western Mosul was close to the location of three houses that were leveled with dozens of civilians inside.

Votel told the House Armed Services Committee Wednesday that the review into the allegations of civilian casualties at the site had transitioned into a more formal investigation.

"It'll be a more formalized approach to really look into the details of this as much as we can to establish what happened, establish what the facts are, identify accountability and then certainly identify the lessons learned out of that," said Votel.

Headed by an Air Force Brigadier General, Votel said the investigation will look at what role the U.S. military and ISIS may have played in the civilian deaths. The intelligence and planning for the airstrike as well as the types of the munitions that were used will also be reviewed.

Votel said he agreed with Lt. Gen. Stephen Townsend's assessment Tuesday that there is "a fair chance that our operations may have contributed to civilian casualties.”

Townsend, the commander of Operation Inherent Resolve, said that it appeared the civilians found at the site may have been placed there as human shields by ISIS.

"I think is also important to clearly recognize that the enemy does use human shields, has little regard for human life and does attempt to use civilian casualty allegations as a tool to hinder our operations," Votel added. "And so they bear responsibility for this as well."

Votel told the committee that there has been no change to the rules of engagement for U.S. airstrikes targeting ISIS.

"We have not relaxed the rules of engagement," Votel said. He explained that last year U.S. Central Command delegated the approval for airstrikes "to the appropriate level" in Iraq in anticipation of the tough urban fight in Mosul.

"To be clear, there were no changes in the rules of engagement that allows us to engage," he emphasized.

A senior military official later explained that in December the delegation of authorizing airstrikes was lowered to more tactical levels reflecting the switch to offensive operations against ISIS in the battle for Mosul. Until then every coalition airstrike had to be approved by a general officer following the rigorous evaluation of a proposed target.

The delegation of authority to lower level commanders has sped up the approval of airstrikes in certain situations, but it has not correlated to more airstrikes said the official. Last week the coalition dropped 700 bombs and used 400 rocket artillery and mortars in western Mosul.

General officers must still approve airstrikes in specific situations like those aimed at ISIS targets located near protected civilian buildings like mosques, schools and hospitals.

The official said delegating the authority for certain airstrikes in the fight for Mosul down to the tactical level enables American advisers accompanying Iraqi troops to more effectively coordinate Iraqi offensive operations.

Iraqi security forces have faced stiff resistance from ISIS fighters as they push into the historic section of western Mosul that is riddled with narrow streets and densely populated areas.

Votel praised Iraqi forces for their resilience in continuing the fight against ISIS despite heavy casualties in western Mosul.

"The Iraqi Security Forces, so far, in about 37 days have sustained about 284 killed and a little over 1,600 wounded in the western part of the city," said Votel. An additional 490 Iraqi forces were killed and 3,000 were wounded in the 100 day battle for eastern Mosul that concluded in mid-January.