Army Chief of Staff Gen. Ray Odierno, who is three weeks away from retirement after 39 years in uniform, expressed his frustration over what has happened to Iraq under the Islamic State.

"It's frustrating to watch it," Odierno, who spent four years in Iraq, said in a Fox News interview published Wednesday. "And I go back to the work we did in 2007, 2008, 2009, and 2010 and we got it to a place that was really good. Violence was low, the economy was growing, politics looked like it was heading in the right direction."

Odierno is viewed as the leader of the Iraq surge. He also suggested between 30,000 and 35,000 American troops stay in the country after the end of 2011 when the U.S. was scheduled to withdraw, a recommendation that was not followed.

"If we had stayed a little more engaged, I think maybe it might have prevented it," he said. "I've always believed the United States played the role of honest broker between all the groups and when we pulled ourselves out, we lost that role."

When asked if it was a mistake for the U.S. to withdraw from Iraq, he replied: "I think it would have been good for us to stay."

Odierno also criticized the decision to cut the Army from 570,000 troops in 2010 to near 490,000 today — a 14 percent reduction. Earlier this month, it was announced the Army would be reduced again by 40,000 troops down to 450,000, though the decision was made two years ago.

"In my mind, we don't have the ability to deter. The reason we have a military is to deter conflict and prevent wars. And if people believe we are not big enough to respond, they miscalculate," Odierno said.

He added: "Two years ago, we didn't think we had a problem in Europe. … [Now] Russia is reasserting themselves. We didn't think we'd have a problem again in Iraq and ISIS has emerged. So, with Russia becoming more of a threat, with ISIS becoming more of a threat, in my mind, we are on a dangerous balancing act right now with capability."

The cuts will have to stop somewhere or they will hamper effective missions, he concluded.