Pakistan finds tunnels in siege area
General: Fighting unknown enemy like 'chasing the shadows'
Pakistanis unsure about 'high value target'
CNN's exclusive video of al-Zawahiri, some of it never before shown.
Did Al Qaeda escape through tunnels?
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) -- The Pakistani military's quest to nab a "high-value target" has suffered a setback with the discovery of a series of tunnels that militants could have used to escape thousands of troops who've laid siege to the area.
The underground passageways extinguished hopes for the quick capture of any "high-value target" who might have been inside the remote, 19-square-mile (50-square-kilometer) part of southern Waziristan province cordoned off by the military.
The battle began last week as part of an antiterrorism campaign by Pakistani troops in the border region. Members of the country's paramilitary Frontier Constabulary ran into trouble during a routine search, which led to the deaths of 15 members of the unit.
Lt. Gen. Safdar Hussein has described confusion on the battlefield, saying troops do not know if the local population is "with us or with them."
"It's very difficult to identify them," he said. "And when an undefined enemy is there, it is practically chasing the shadows."
The longest of the tunnels, said to be about a mile (1.6 kilometers) long, runs from the houses of tribesmen Nek Mohammed and Sharif Mohammed, and ends near the Afghanistan border, officials said.
A spokesman for Pakistan's Office of Security for the Federally Administered Tribal Areas said the longest tunnel was previously undiscovered, and the Pakistani military has surrounded its exit.
Meanwhile, unknown forces killed eight Pakistani soldiers in an ambush on a military convoy Monday en route to resupply troops involved in the nearly week-long confrontation, military officials said.
The rocket attack occurred some distance from the standoff in the mountainous region along Pakistan's northwest border.
On Sunday, Pakistani tribal leaders began efforts to broker an end to the fighting.
They met early Sunday with Pakistani military officials and persuaded the army to cut back its air assault on the region, military sources said.
In return, the tribal leaders agreed to enter the area and try to persuade the Ahmed Zai tribe to hand over captives and any militants they may be protecting, the sources said. (Full story)
Meanwhile, speculation persisted about who the fighters -- including local tribesmen -- might be protecting.
The fighting attracted global attention when Pakistani officials -- expressing surprise at the ferocity of the resistance suggested the fighters could be protecting al Qaeda's No. 2 man, Egyptian doctor Ayman al-Zawahiri.
But after initially dropping broad hints that they believed the target was al-Zawahiri, the Pakistanis backed off the claim last weekend, saying it could be an Uzbek or Chechen commander, or even a local criminal.
"It can't be said with certainty who here and who's not here," army spokesman Maj. Gen. Shaukat Sultan said.
CNN's Ash-har Quraishi and Nic Robertson contributed to this report.