Al-Qaeda's number two Ayman Zawahiri called Thursday on Pakistanis to support jihadists in the country's tribal areas, saying it was 'the' battle against the American 'crusaders,' said the US-based SITE Intelligence group. Zawahiri's comments were delivered in a video called 'Path of Doom' posted on jihadist websites and monitored by SITE, a private group that follows jihadist activities on the Internet. 'The war in the tribal areas and Swat is an inseparable part of the Crusaders' assault on the Muslims the length and breadth of the Islamic world,' Zawahiri was quoted as saying. '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,' he said. He argued that the US military was using the Pakistani army as its proxy in the tribal areas and Swat as a means to defeat the insurgency in neighboring Afghanistan. The video, which SITE said was produced by Al-Qaeda's media arm as-Sahab, took the form of a 22-minute, 30-second documentary with English subtitles. Zawahiri appeared with a bookshelf to his back as he has in previous videos. Its release follows the killing of Baitullah Mehsud, the leader of the Pakistani Taliban and an Al-Qaeda ally, in a US missile strike, and reports of a struggle to succeed him. Hakimullah Mehsud, a young commander, this week claimed leadership of the militant group. US drone attacks in the tribal areas have intensified this year, with the latest one on Thursday reportedly killing eight Taliban militants in the northwestern Khyber tribal region. 