Hayden told NBC' "Meet The Press" the military efforts led by Iraqi Prime Minister Nouri al-Maliki were necessary to help the Iraqi government regain control of the country.

"This was inevitable, this had to be resolved, we just can't have the second major city in the country -- economically, the most important city in the country -- beyond the control of the government until -- although, you know, there is a certain sense of ... 'disappointment' in that the fact that violence is increasing," Hayden said. "We knew we couldn't get to where we had to be for the Iraqi state, from a modern, democratic Iraqi state, without going through this."

Hayden also downplayed U.S. involvement in the military action against Shiite militants in the city, saying Iraqi forces should be the key to rebuilding Iraq.

"What you need is combat power that is competent and evenhanded and that, over time, we would expect more and more of that definition to be met by Iraqi security forces," Hayden said.