Al-Qaeda leader Ayman al-Zawahiri released a video coinciding with the anniversary of the September 11 attacks, confirming for the first time the death of his deputy, US monitors said.

The 42-minute video confirms that Abu Yahya al-Libi was killed in a drone strike in Pakistan's Waziristan tribal area on June 4, according to the SITE and IntelCenter monitors.

Libi was known as Al-Qaeda's global propaganda mastermind and his death dealt the biggest blow to the group since the killing of Osama bin Laden by U.S. special forces in May 2011, AFP reported.

"With the martyrdom of Sheikh Abu Yahya, may Allah have mercy on him, people will flock even more to his writings and call, Allah willing," Zawahiri said in Arabic, according to a SITE translation.

The video was posted on jihadist forums on Monday, the U.S. monitors said.

While it does coincide with the anniversary of the September 11, 2001 terrorist attacks, the video does not explicitly or directly address the issue.

Zawahiri does, however, single out President Barack Obama for being a "liar" who was elected to "trick" Muslims around the world, but who nevertheless is "being defeated in Afghanistan," AFP reported.

He also mentions Warren Weinstein, an elderly American aid worker kidnapped in Pakistan by Al-Qaeda just over a year ago, vowing to keep him in captivity until U.S. forces release al-Qaeda prisoners held in Afghanistan.

Entitled "The Lion of Knowledge and Jihad: Martyrdom of al-Sheikh Abu Yahya al-Libi", the video is Zawahiri's 13th statement in 2012.

Libi, a jihadist theologian, became a major motivational figure for Al-Qaeda followers after he escaped from U.S. custody in Afghanistan in 2005.

A video featuring Libi was released by Al-Qaeda a week after his death, AFP reported.