WASHINGTON (NewsNation) — Gen. Kenneth McKenzie Jr., the chief of the U.S. Central Command who oversaw the withdrawal of U.S. troops from Afghanistan last summer, is retiring.

Mckenzie headed CENTCOM, the military’s command over the Middle East, since 2019. The command covers more than 4 million square miles and includes 560 million people. He previously served as director of the Joint Chiefs of Staff.

McKenzie led the Biden administration’s controversial evacuation of remaining American troops and allied Afghans from the country last year, which was quickly taken over by the Taliban. The general had continuously expressed hesitancy about the quick exit but ultimately carried out the president’s August 31st deadline.

In his last Pentagon briefing Friday, he said there isn’t a day that goes by that he doesn’t think about the 13 American soldiers killed in a suicide attack on Kabul airport during the withdrawal. However, he said he doesn’t know “what we could have done” to prevent it.

McKenzie warned Friday that although CENTCOM is transitioning from long wars in Iraq and Afghanistan, Iran poses an imminent threat, calling it “the greatest threat to regional security and stability.”

McKenzie said he believes the threat in Afghanistan is still a major concern as well, citing ISIS’s “highest priority” is to carry out an attack in the United States. This ISIS affiliate in Afghanistan was responsible for the Kabul attack and considered by US intelligence officials to be the most active threat in the region.

He reiterated Friday that the terrorist group “aspires to attack the United States, but will need 12 to 18 months to regenerate for external attacks outside of Afghanistan.”

“There are days I would rather have my leg taken off below the knee than come in and talk to your guys,” Mckenzie said in his final remarks to reporters. “I still very much appreciate your efforts to document and report out our activities to the American public.”

McKenzie is slated to be replaced by Army Lt. Gen. Michael “Erik” Kurilla in the coming weeks.