Pakistani officials, who spoke to the Associated Press on condition of anonymity, said intelligence indicated the Egyptian-born al-Zawahri has been cornered in an operation that began Tuesday in South Waziristan, near the Afghan border, and involved hundreds of troops and paramilitary rangers.
"We have been receiving intelligence and information from our agents who are working in the tribal areas that al-Zawahri could be among the people hiding there," a military official said. "All of our efforts are to capture him."
An intelligence official and a senior politician in President Gen. Pervez Musharraf's government both confirmed the account. The intelligence official said information was also coming in from some of the 18 suspects arrested during Thursday's operation. He said some of the suspects had said al-Zawahri was injured in the operation, which left "dozens" dead.
In an interview with CNN, Musharraf said he'd spoken with the commander of Pakistani troops in the region. He said the commander reported "fierce resistance" from a group of fighters entrenched in fort-like buildings, and that there were indications that a senior figure was surrounded.
"He's reasonably sure there's a high-value target there," Musharraf said.
Speaking on the condition of anonymity, a U.S. counterterrorism official said: "It would appear that the Pakistanis have surrounded a very senior al Qaeda figure, but at this point we are not certain who it is."
CBS News Correspondent Mark Knoller, who is with President Bush at Ft. Campbell, Ky., quotes a White House spokesman as saying he is aware of the reports that a high-level al Qaeda figure has been surrounded near the Pakistani-Afghan border, but that the administration has no independent confirmation.
A spokesman for the U.S. military in Afghanistan told the AP that it was hoped Pakistani forces had indeed cornered al-Zawahri, but that he had no new information on the whereabouts of either of the al Qaeda leaders.
Also in Afghanistan Thursday, two American soliders were killed and two more wounded in what U.S. Central Command called anattack in a village near Tarin Kowt. The attack was not believed to be linked to fighting over al-Zawahri.
Al-Zawahri, 52, is a physician and the founder of the Egyptian Islamic Jihad. He has been called the second most-wanted man in the world and the brains behind al Qaeda.
Many believe he was the operational mastermind behind the attacks on Sept. 11. 2001. He's been indicted for his alleged role in a string of attacks, including the 1998 bombings on U.S. embassies in Africa that killed more than 200 people.
Al-Zawahri has shown up on audio and videotapes and he's been seen walking the rugged mountains of Afghanistan with bin Laden. Both men have escaped U.S. and coalition forces that have tried everything from cave-to-cave searches to high-tech surveillance.
A $25 million reward exists for al-Zawahri's capture.
The Pakistani military has been pursuing 100 tribal leaders, whom authorities want to roll into their efforts to hunt al Qaeda in the Waziristan frontier. So far, about two-thirds have said they'd provide information and turn over any Islamic militants in their territories, American defense officials said on condition of anonymity.
The others face destruction of their homes by the Pakistani military, officials said.
The Pakistanis also are targeting Arabs and other foreigners who settled in the tribal regions shortly after the Afghan-Soviet war in the 1980s, the officials said. While some veterans of the war formed the nucleus of al Qaeda, others put down roots in Pakistan.
It is believed that some of these veterans are providing a support network for bin Laden and his followers in the region, officials said.
U.S. officials say they are watching to see if the Pakistani actions send militant fighters moving back to Afghanistan, where U.S. troops operate freely.
Hundreds of Pakistani troops have moved into three South Waziristan towns — Azam Warsak, Shin Warsak and Kaloosha — firing artillery and using helicopter gunships against entrenched positions.
"They are not coming out in spite of the fact that we pounded them with artillery," Musharraf told CNN.
Early morning calls from mosques warned residents in Azam Warsak, Shin Warsak and Kaloosha to leave the area, apparently to give the troops more room to operate.
"They asked locals, women and children, to move out, which many did. And then they shot upon the area, with ... helicopters also," Musharraf told CNN.
At least 41 people — including 15 soldiers and 26 suspected militants — were killed Tuesday in fighting in the area, and army spokesman Gen. Shaukat Sultan said there were an unknown number of casualties in continuing action Thursday.
The military said Thursday that most of those killed were foreigners, but it did not give their nationalities and acknowledged that only two bodies had been recovered.
The two dead were believed to be a Chechen and someone of Middle Eastern origin, a military official said on condition of anonymity.
The news came the same day as U.S. Secretary of State Colin Powell announced in Islamabad that Washington was bestowing the status of "major non-NATO ally" on Pakistan, and praised the country for its help in the war on terror.
Powell, who left the country hours before the announcement, also said he believed there was evidence that bin Laden is still alive and hiding in the rugged border area.
"No one has seen him, so how can one be sure?" Powell told Geo TV. "But he has certainly given evidence that he is alive and active. But we can't be sure.