CAIRO, Egypt -- A tape purportedly recorded by Ayman al-Zawahri, the No. 2 figure in the al-Qaida terror group, called Pakistani President Pervez Musharraf a "traitor" Thursday and urged people to overthrow his government.
The pan-Arab satellite channel Al-Jazeera broadcast a seven-minute excerpt from a tape it received Thursday. Its authenticity could not immediately be verified, but the speaker sounded like al-Zawahri and made references to the Islamic holy book, the Quran, which is known to be al-Zawahri's style.
The speaker also called for a military uprising in Pakistan.
"Musharraf seeks to stab the Islamic resistance in Afghanistan in the back," the speaker said.
"Every Muslim in Pakistan should work hard to get rid of this client government, which will continue to submit to America until it destroys Pakistan."
Pakistani Foreign Ministry spokesman Masood Khan said the government has no immediate comment on the purported al-Zawahri tape. When an al-Zawahri tape released in September called for Musharraf's overthrow, the government said it would not be deterred in its pursuit of terrorists.
The tape comes as Pakistani troops are in the second week of a campaign along the Afghan border in South Waziristan, a longtime hiding place and stronghold of Islamic militants from al-Qaida, Afghanistan's Taliban and their Pakistani supporters.
It was not known when the tape was made, but the speaker appeared to be referring to the conflict in South Waziristan when he said, "I call on the Pakistani army: you, poor army, what a miserable state Musharraf has put you in ... Musharraf ruins your natural fences -- those tribes on the border -- by engaging you in a fight with them. Then he removes your nuclear weapons.
"Will you stay silent until Pakistan is divided again?"
The speaker repeatedly named the Pashtun and Baluch border tribes and urged them to close ranks with the Taliban against the Pakistani army.
"Taliban and their supporters are your brothers," the speaker said, "so how can you allow the agents of crusaders and Jews to hurt them?"
He used the word "crusaders" for Americans as Islamic militants often do.
The speaker said such military operations on the borders violated Islamic law by pitting Muslims against each other at America's bidding.
"Every soldier who finds this act to be legitimate is an infidel, according to Islamic law," the speaker said.
After Musharraf spoke hopefully of capturing a "high-value target," there was speculation that al-Zawahri might be in the rugged border area where local tribes have more power than the Pakistani federal government.
Pakistan Interior Minister Faisal Saleh Hayyat said Thursday that more than 50 terrorists have been killed in the operation. More than 150 suspects have been captured, said Brig. Mahmood Shah, chief of security in Pakistan's tribal areas.
The speaker did not mention Israel's Monday morning assassination of Hamas founder Sheik Ahmed Yassin, which suggests the tape was recorded before then.
Al-Jazeera spokesman Jihad Ballout said the Qatar-based channel received the tape Thursday, but he declined to reveal how. The tape is 17 minutes long.
"Indications are that it is authentic," Ballout said, "the voice, the nuances."
In the United States, an intelligence official said the CIA was reviewing the tape to determine whether it was authentic. He spoke on condition of anonymity.
Vince Cannistraro, a former CIA counterterrorism chief, said the rapid response of the tape suggests that Al-Zawahri was nowhere near the Pakistani fight zone. He said the message was essentially a call to kill Mussharref.
A Cairo expert on Islamic militants, Dia'a Rashwan of the Al-Ahram Center for Political and Strategic Studies, said the tape indicated al-Zawahri was close to the action in South Waziristan.
"This is a counterattack. It reflects how he can feel the tremendous security effort exerted at the borders," Rashwan said.
In urging the tribes to rally to his side, al-Zawahri seems to realize that the Pakistanis are much more dangerous for him than the Americans, Rashwan said.
The speaker also urged Islamic clerics to tell the Pakistani people "the truth about Musharraf, the traitor and killer of Muslims."
"They should incite the nation to expel the crusaders from Pakistan," the speaker said.
"The crusade in Afghanistan, Iraq, Chechnya and Palestine is targeting Pakistan primarily, because America does not want Pakistan to be a special power in the center of Asia."
Al-Zawahri is believed to have provided much of the ideology driving al-Qaida since his Egyptian Islamic Jihad merged with Osama bin Laden's network in 1998, experts say. The United States has offered a $25 million reward for his capture.