Tim Armstrong, the chief executive of AOL, issued an unusual apology on Tuesday to his entire staff for the public manner in which he fired an employee during an internal conference call last Friday.

A recording of the firing was leaked to news outlets and caused a firestorm around Mr. Armstrong, who has been trying to turn AOL from a struggling Internet portal into a successful media company.

The four-paragraph statement, sent to AOL employees at 4:30 p.m. and obtained by The New York Times, said, “I am writing you to acknowledge the mistake I made last Friday during the Patch all-hands meeting when I publicly fired Abel Lenz. It was an emotional response at the start of a difficult discussion dealing with many people’s careers and livelihoods. I am the C.E.O. and leader of the organization, and I take that responsibility seriously.”