Battle rages with al Qaeda fighters
Reports: Bin Laden's alleged lieutenant may be surrounded
The U.S. is downplaying the possibility of the capture of Ayman al-Zawahiri.
A swift interrogation would follow if al-Zawahiri is caught.
CNN's exclusive video of al-Zawahiri, some of it never before shown.
The Pakistan border is akin to the 'Wild West.'
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Watch CNN for ongoing reports, updates and analysis of the operation on the Pakistani-Afghan border.
Position: Osama bin Laden's closest adviser
Status: Wanted, $25 million reward
Background: Medical doctor; founder of Egyptian Islamic Jihad; referred to as the "brains of al Qaeda"
ISLAMABAD, Pakistan (CNN) -- Pakistani forces are meeting fierce resistance in a battle with al Qaeda fighters in a mountainous region near the Afghan border.
It is believed the terror network's reputed second-in-command, Ayman al-Zawahiri, may be holed up in the remote area, Pakistani officials said.
The fighting has raged for several days in northwestern Pakistan, and government sources said the their troops have suffered significant casualties.
They said the 300 to 400 al Qaeda fighters and allied tribesmen have the high ground, making it easier to defend against the Pakistani troops.
Helicopter gunships and fighters were expected to pound the mountain peak later Saturday.
"The mission is to get these people dead or alive," Maj. Gen. Shaukat Sultan told reporters.
The battles are taking place in remote areas of southern Waziristan, on Pakistan's border with Afghanistan, where thousands of Pakistani forces have cordoned off 19 square miles (50 square kilometers) with two lines of defense, officials said.
Sultan said there is no way for the al Qaeda forces to escape.
"That has been effectively sanitized," he told CNN's Aaron Brown in Islamabad. "It has been cordoned and the army should not take long to flush it out."
When pressed for a timetable, Sultan would only say the battle would be over "very soon."
Al Qaeda's well-trained and well-equipped fighters were defending their positions with mortars, rocket-propelled grenades and heavy gunfire, officials said.
So far the battle had included little close combat, they said.
U.S. officials have declined to comment on whether Predator surveillance drones are aloft in the area -- or that spy satellites are focusing attention on it -- but they did say that they are providing any assistance that the Pakistanis have requested.
For weeks, knowledgeable sources confirmed, a small team of American intelligence professionals and military personnel have been providing real-time intelligence and communications assistance.
Pakistani President Pervez Musharraf has told CNN that the fierce resistance his forces had encountered was a sign that someone was being protected.
"They are not coming out in spite of the fact that we pounded them with artillery," he said. He did not name the figure being protected, but said it may be a "high-value target."
Speaking to CNN on Friday morning, Pakistan Information Minister Sheikh Rashid Ahmed was wary of providing more details, noting that al Qaeda is monitoring television and newspaper reports.
"They never surrender, the al Qaeda people," Ahmed said. "They like to fight and they like to die there, so the only thing I can say is, we have to wait and see."
Al-Zawahiri considered top al Qaeda lieutenant
Al-Zawahiri, an Egyptian national, is considered by U.S. intelligence to be Osama bin Laden's closest adviser. U.S. officials believe bin Laden may be within miles of al-Zawahiri.
National security adviser Condoleezza Rice said al-Zawahiri's capture would be a "major step forward" in the war on terrorism, but added, "We have to dismantle the entire network, not just one person."
The United States is offering a $25 million reward for al-Zawahiri. U.S. officials believe if he were captured, they could likely work out a deal with Pakistan to have him turned over to U.S. custody.
U.S. officials have long said they believe bin Laden and al-Zawahiri are probably in Pakistan near the border with Afghanistan.
The two have slipped away before, surviving a U.S. onslaught on the Tora Bora region of Afghanistan in December 2001.
Meanwhile, in a videotaped message delivered to the Arabic-language network Al-Jazeera, a spokesman for the Taliban -- Afghanistan's former rulers and allies of al Qaeda -- vowed to respond in kind to the operations.
"The Pakistanis have deceived us in a way that will never be forgotten," said Abdul Latif Hakimi, who appeared in the video with his face covered.
Hakimi also pledged to "attack the American forces if they attack us on either side of those borders."
However, the authenticity of the videotape was in question. The Reuters news agency said it had spoken with Hakimi and he denied issuing any such statement.