Zawahiri's 42-minute video was posted on Jihadi websites prior to the anniversary of the Sept. 11, 2001, terror attacks on the United States, Britain's Daily Telegraph reported, citing U.S. monitoring groups.
Zawahiri became the top leader of al-Qaida, succeeding Osama bin Laden who was killed last year by U.S. Navy SEALs during a raid on his compound in Pakistan.
In the video, the Telegraph said Zawahiri, who is believed to be hiding in Pakistan's tribal regions, referred to Libi by his birth name and said he was proud to announce "the news of the martyrdom of the lion of Libya Sheik Hassan Mohammed Qaed."
The Telegraph said the U.S. government had announced the death in June of Libi, who had escaped from a high-security prison in Afghanistan in 2005. The death of Libi, al-Qaida's chief propagandist, was seen as a huge loss to the terror group.
Zawahiri also was quoted as saying U.S. President Barack Obama has been defeated in Iraq and Afghanistan.