"CBS This Morning" co-host Charlie Rose said on the network's "Face the Nation" Sunday, Assad issued the denial in an interview at the Presidential Palace in Damascus.
"Well, he denied that he had anything to do with the attack," Rose said. "He denied that he knew, in fact, that there was a chemical attack, notwithstanding what has been said, and notwithstanding the videotape [showing apparent victims of the attack in various stages of illness and distress.]"
Rose said Assad told him the available evidence is not sufficient "to make a conclusive judgment."
The interviewer said Assad would neither confirm or deny Syria has chemical weapons, but said if the regime does possess them, "they're in centralized control, so no one else has access to them."
Rose said Assad repeated a suggestion rebels in Syria had something to do with the Aug. 21 attack.
He said Assad did not know whether to expect a military strike by the United States but he assumed there will be.
"He said we're prepared as best we can," Rose said.
The interview -- Assad's first interview with CBS in nearly two years -- will be aired in its entirety Monday on the "Charlie Rose Show" on PBS. Portions will be aired Monday on "CBS This Morning" as well as on CBSNews.com and the "CBS Evening News with Scott Pelley."