Retired U.S. Army Gen. David Petraeus speaks during a Senate Armed Services Committee hearing on Capitol Hill September 22, 2015 in Washington, DC.

Former CIA chief and retired general David Petraeus on Tuesday said America should take a more active role in the Syrian crisis, including implementing no-fly zones to prevent regime planes dropping barrel bombs.

Speaking before the Senate Armed Services Committee, Petraeus said the U.S.-led coalition fighting the Islamic State of Iraq and Syria (ISIS) had made “inadequate” progress in Iraq and Syria and said the Syrian civil was a “geopolitical Chernobyl.”

“The fallout from the meltdown of Syria threatens to be with us for decades,” he said. “The longer it is permitted to continue, the more severe the damage will be.”

Central to Petraeus’s testimony on Syria was the dilemma Western politicians face with regard to President Bashar Al-Assad.

The United States does not want him in power in the long run, but neither does it want his ouster without knowing who or what would replace his regime.

“The problems in Syria cannot be quickly resolved. But there are actions the U.S. and only the U.S. can take that would make a difference. We could, for example, tell Assad that the use of barrel bombs must end. And that if they continue, we will stop the Syrian air force from flying. We have that capability,” Petraeus said.

“This would not end the humanitarian crisis in Syria … it would remove a particularly vicious weapon from Assad’s arsenal.”

He also said he would support the creation of secure enclaves in Syria to protect the battered civilian population.

Petraeus began his testimony with an emotional apology over his spectacular fall from grace, after he pleaded guilty this year to providing classified secrets to his mistress.

“Four years ago, I made a serious mistake, one that brought discredit on me and pain to those closest to me,” he said.

“There’s nothing I can do to undo what I did. I can only say, again, how sorry I am.”

He was given two years’ probation and a $100,000 fine.

Petraeus became a household name in the United States when he oversaw the troop “surge” in Iraq in 2007, and U.S. leaders credited him for salvaging the troubled war effort.

He resigned from the CIA in 2012.