(CNN) -- Al Qaeda's second-in-command called on Pakistanis to back Islamic militants in the country's tribal areas against what he called an ongoing assault by American "crusaders" and the Pakistani army.
Al-Qaeda's second-in-command, Ayman al-Zawahiri appears in a video released on September 2, 2006.
Punishment from God was promised for Muslims who did not follow the words of Ayman al-Zawahiri in a video that appeared on radical Islamist Web sites Thursday.
"The war in the tribal areas and Swat [Valley] is an inseparable part of the crusaders' assault on the Muslims the length and breadth of the Islamic world," al-Zawahiri said in the video, titled "Path of Doom."
"This is the battle, briefly and plainly; and this is why anyone who supports the Americans and Pakistan army -- under any pretext, ploy or lie -- is in fact standing with, backing and supporting the crusaders against Islam and Muslims."
The Pakistani military is fighting Taliban militants in the country's north, and missile attacks from suspected U.S. drones have targeted militant leaders -- one of them killing Baitullah Mehsud, the leader of the Pakistani Taliban.
Reports from the region suggest government troops have dislodged the Taliban from many areas of the North West Frontier Province, but militant attacks continue daily.
In the video, Al-Zawahiri suggested that the United States has wider goals in the region.
"They want to eliminate the Mujahedeen (Islamic militants) in the tribal areas so they can seek to smother the Jihad in Afghanistan," he said.
NATO-led forces are battling the Taliban across the border in Afghanistan as well. U.S. and British forces launched offensives in Helmand province this summer.
Al-Zawahiri warned Muslims that they have a religious duty to support the jihad, or struggle, or face punishment from God.
"No people abandons Jihad without Allah giving them a general punishment," he said, quoting the Quran.
Al-Zawahiri also prayed for the annihilation "the Americans and Jews" and anyone who might help them.