The United States could have prevented the rise of the Islamic State group and the resultant chaos in the Middle East, General Raymond Odierno, the current Chief of Staff of the U.S. Army, said Tuesday. Odierno, who is set to retire as army chief in August, said that it is “frustrating” to watch the growing threat of ISIS in the Middle East, where the U.S. Army once achieved significant gains.

In an interview with Fox News, Odierno talked about several topics, ranging from the Iran nuclear deal and the U.S. Army’s plan to cut 40,000 troops owing to a shrinking budget. But he emphasized the growing concerns from the rise of ISIS in Iraq and Syria, suggesting more effective preventive measures should have been taken as the fall of large parts of Iraq to the extremist group was not unavoidable.

“If we had stayed a little more engaged, I think maybe it might have been prevented,” Odierno told Fox News. “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.”

Odierno expressed his concerns about the deep cuts to the U.S. Army at a time when ISIS is turning out to be a growing threat in the Middle East, even as Russian military movements along its border with Eastern Europe have escalated tensions in the region.

“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,” Odierno said.

On the recently announced nuclear deal with Iran, Odierno said that though he supported the controversial agreement, he does not expect Iran to change its behavior in the Middle East.

“Iran has continued to do malign activities throughout the Middle East [and] they will continue,” Odierno said, accusing Iran of contributing to the unrest in Iraq and the rise of ISIS.