Osama bin Laden will soon release a new message declaring war on Pakistani President Pervez Musharraf, according to Islamist websites.
Mr Musharraf is a key ally in the US "war on terror", despite widespread opposition among the Pakistani population.
The declaration of war from Islamist al-Qaeda comes at a time when he is facing intense domestic pressure.
Meanwhile, the terror network issued another propaganda tape today claiming that Islamic militants are defeating the United States in Afghanistan and Iraq.
Islamist websites are carrying banners stating: "Soon, God willing: 'Come to Jihad (holy war)', from sheik Usama bin Laden, God protect him... Urgent, Al Qaeda declares war on the tyrant Pervez Musharraf and his apostate army, in the words of Osama bin Laden".
Meanwhile the SITE Intelligence, a group that monitors Islamist websites, said: "The SITE Intelligence Group has learned that a new message is forthcoming from the head of al-Qaeda, Usama bin Laden, and titled, 'Come to Jihad'.
"Images of deceased jihadi leaders in Pakistan and Waziristan, Abdul Rashid Ghazi, Nizamuddin Shamzai, Nek Muhammad and Abdullah Mahsud, appear in the announcement.
"A message posted with the announcement indicates that the message will address the people of Pakistan."
IntelCenter, another US outfit monitoring Islamist websites, said the video or audio message, entitled 'Come to Jihad,' is expected to be released by al-Qaeda's media arm Al-Sahab in the next 72 hours.