A banner warning of the upcoming message was posted on the site, which frequently airs Al Qaeda videos. Wednesday's notice did not specify whether the new message was a video, audiotape or text, but al-Zawahiri usually releases videos.
His latest came earlier this month, to coincide with the fifth anniversary of the Sept. 11 attacks. Al Qaeda released a string of videos for the anniversary, showing increasingly sophisticated production techniques in a likely effort to demonstrate that it remains a powerful, confident force despite the U.S.-led war on terror.
Usama bin Laden and his deputy al-Zawahiri are believed to be hiding in the Afghan-Pakistan border region. Many analysts believe that they no longer have centralized control to order or organize attacks by militants around the world. The capture and killing of many midlevel commanders has left Al Qaeda more diffuse and amorphous.
But at the same time, the terror network's propaganda machine has grown more sophisticated, aiming to rally militants and romanticizing jihad, or holy war.
The banner did not give a specific time, saying only that al-Zawahiri would release a message about the pope, Bush and Darfur "soon, God willing."
Pope Benedict XVI angered the Muslim world in a speech in Germany on Sept. 12, when he quoted a 14th century Byzantine emperor as saying: "Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached."
Benedict has expressed regret for offending Muslims by his remarks and said they did not reflect his personal views, but he has not offered a complete apology as some had sought.