In a video message posted on an Islamic website Saturday, al-Zawahiri called on the Pakistani military to help fight the government of President Pervez Musharraf. Al-Zawahiri said every soldier should disobey orders to kill Muslims in Pakistan and Afghanistan.
The Egyptian militant also said the U.S.-led coalition in Iraq has achieved nothing but losses, disasters and misfortune in three years of war.
Al-Zawahiri is believed to be hiding in the mountainous areas of Afghanistan or Pakistan.
The U.S. State Department said it was aware of the video, but had no comment on its contents or authenticity.
The Egyptian militant's message comes in the same week as broadcasts by two other senior al-Qaida leaders.
An audiotape from Osama bin Laden was broadcast Sunday on al-Jazeera. Bin Laden accused the West of waging what he called a "crusader-Zionist war" against Muslims. He also said Westerners were complicit in the actions of their governments, a statement analysts say is meant to justify terrorist attacks on civilians.
A video released Tuesday by al-Qaida in Iraq leader Abu Musab al-Zarqawi ridiculed the new Baghdad government and vowed that his guerrillas will defeat the U.S.-led coalition in Iraq.
Some information for this report was provided by AFP, AP and Reuters