Adam Gadahn, who commonly delivers the terror organization's English messages, said the extremist network was being framed for the bloodshed by the U.S. and Pakistani intelligence services.
"The perpetration of such deplorable acts and the pinning of responsibility for them on the mujahedeen only serves the enemies of Islam and Muslims, who are today staring defeat in the face," he said, blaming the "puppet media" for implicating Al Qaeda in the attacks.
"The mercenaries of the ISI, RAW, CIA or Blackwater are the real culprits behind these senseless and un-Islamic bombings," he added.
The ISI and RAW are the Pakistani and Indian intelligence agencies, respectively, while Blackwater is the private security firm — now called Xe Services — whose involvement in the killings of Iraqi civilians have tarnished its reputation throughout the Muslim world.
More than 500 people have died in a slew of attacks in Pakistan that began in October, just as the Pakistani army started waging a ground offensive against the Taliban in South Waziristan, a tribal region bordering Afghanistan.
A single truck bomb in the northwest city of Peshawar killed more than 100 people at a market that sells mostly women's clothes and children's toys. More recently, twin bombs at a similar market in the eastern Pakistani city of Lahore killed nearly 50.
Pakistani authorities have laid blame for the recent spate of attacks on the Pakistani Taliban or their affiliates, which include Al Qaeda and other local militant groups.
Such groups, which analysts say are increasingly intertwined, most often to attack security targets. But the militants generally avoid claiming responsibility for assaults that kill a large number of civilians.
In a transcript of the video released by the SITE Intelligence Group, a Washington-based monitor of militant Web sites, Gadahn told Pakistanis their real enemies were secular regimes, corrupt police, judges and tribal nationalists.
Gadahn's message may resonate in Pakistan, where conspiracy theories are rife, support for militancy has only recently taken a downturn and anti-Americanism is widespread.
After the market blast in Peshawar, many Pakistanis expressed disbelief that Islamist groups could have attacked other Muslims in such a manner. And in some corners of the Pakistani media, Blackwater has increasingly been floated as a culprit in nefarious events.
Gadahn grew up in Los Angeles and then moved to Pakistan in 1998, according to the FBI. He is said to have attended an Al Qaeda training camp six years later, serving as a translator and consultant for the group.
Al Qaeda's media arm, al-Sahab, is increasingly using English-language videos to address Muslims in Pakistan who are unlikely to speak Arabic. Gadahn's message specifically addressed Muslims in south Asia, including India, Pakistan and Bangladesh.