Thousands of Pakistani army reinforcements joined in an ongoing offensive Friday to home in on a "high value target" that may be Usama bin Laden's No. 2 man, as fighting intensified to root out Al Qaeda (search) and Taliban fugitives from their hiding places.

Ayman al-Zawahri (search) — bin Laden's deputy and the man considered the brains behind the Al Qaeda terror network — is believed to be cornered and perhaps wounded somewhere within a 3-square mile area of Pakistan near the rugged Afghan border.

There was no indication that bin Laden was with the Egyptian-born al-Zawahri, but the Pakistani military estimates that about 400 militants — a mix of foreigners and Pakistani tribesmen — are cornered in the border battle.

Wajahat Malik, a journalist in Pakistan told Fox News that at one point during the fighting Friday "10 terrorists tried to make a run from their hideout, one was gunned down by the troops and the rest ran back ... the body is still laying there."

Shortly after, another Pakistani journalist, Hamid Mir, told Fox News the fighting "is highly intensified and a bloody battle is going on.

"Pakistani troops have surrounded a group of 40 or 50 people who have taken position on a mountain," he said. The militants are "trying to get a dead body of a terrorist who was killed, but the terrorists are doing their best to protect the dead body ... We don't know who this dead man is."

But a Taliban spokesman, Abdul Samad, told The Associated Press by telephone that al-Zawahri and bin Laden were hiding in Afghanistan, far from the Pakistani assault.

"Muslims of the world — don't worry about them, these two guests, they are fine," Samad said.

Hundreds of civilians poured out of the battle zone in the tribal South Waziristan region, some wounded and others carrying meager possessions — clothes, carpets, pots and pans. Many said they knew nothing about the militants in their midst, and expressed outrage at the army assault.

Authorities hoped to wrap up the raid "during the next 48 hours," by Sunday afternoon, Interior Minister Faisal Saleh Hayyat told The Associated Press. Dozens have been killed in the four-day operation.

The Pakistani forces were joined by "a dozen or so" American intelligence agents who were "assisting Pakistan in technical intelligence and surveillance," said Army spokesman Gen. Shaukat Sultan.

Across the Afghan border a few miles away, U.S. and Afghan forces tightened a net along the rugged frontier and have arrested midlevel terrorist leaders in recent days, authorities said.

In Pakistan Friday, Sultan told a news conference that "from the type of resistance" they are battling, "the militants could be anything from 300 to 400."

"The type of resistance, the type of preparation of their defensive positions, the hardened fortresses they have made means we can assume that there could probably be some high-value target there," he said.

He disputed claims by four senior Pakistani officials that captured militants had revealed that al-Zawahri was there, and possibly injured.

"So far, whatever people we have apprehended, we have not got confirmation from them," he said, but added: "Even if we knew more, we couldn't tell you."

Fighting spread Friday to two more villages in South Waziristan, where hundreds of paramilitary forces began an operation against Al Qaeda and Taliban fugitives four days ago.

Townspeople said heavy guns fired through the night and they saw jet fighters in the area, although it wasn't clear if the aircraft had opened fire.

On Thursday, Pakistani President Gen. Pervez Musharraf (search) said a "high value" target was believed trapped, and three senior Pakistani officials said that intelligence indicated it was al-Zawahri.

Information Minister Sheikh Rashid Ahmed said Friday the siege was "narrowing down," and that the target could be identified as troops get closer. "They (the militants) are giving a tough contest. They have built bunkers in their homes," he said.

Pakistani troops sealed escape routes and used artillery and helicopter gunships to attack militants near the rugged Afghan border.

Residents reported seeing scores of military trucks, carrying troops and weapons, including light artillery and heavy machine-guns, and some armored vehicles. Army troops took up positions on rooftops of private homes to provide security for the convoy of troops moving from Wana to the target areas.

Someone claiming to be a Taliban spokesman threatened Friday that the group would attack U.S. and Pakistan forces if they did not stop fighting the militants, Reuters reported.

But soon after the tape aired on Al Jazeera, Taliban spokesman Abdul Latif Hakimi told Reuters: "None of the Taliban spokesmen have issued any statement like that."

'Major Step Forward'

Condoleezza Rice, President Bush's national security adviser, told Fox News Friday that if al-Zawahri were captured, it would be "a major step forward" in the war on terrorism.

"It is always a good thing to capture a major Al Qaeda leader," she said. "It does damage to the organization ... but the capture of one man is not going to destroy Al Qaeda."

Chairman of the Joint Chiefs of Staff, Gen. Richard Myers, told Fox News that U.S. officials still don't have a clear picture of what's happening or who exactly is being targeted.

Calling Pakistan a "very good partner in this war on terrorism," Myers noted that the terrain in the tribal areas is difficult, the indigenous people aren't "particularly friendly" and the border isn't recognized.

U.S. counterterrorism officials told Fox News that the United States military is providing surveillance assistance to the Pakistanis in the Waziristan operation. This likely includes unmanned predator drones, satellite technology and perhaps spy planes.

'They Are Not Coming Out'

Pakistani forces battled with hundreds of militants in five villages near South Waziristan's main town of Wana, pounding fortress-like mud-brick compounds as entrenched suspects fought back. An intelligence official said "dozens" were killed Thursday, and some of their hide-outs had been flattened.

At least 41 people — 15 Pakistani soldiers and 26 suspected militants — were killed earlier this week in fighting in the area.

This semiautonomous tribal region, which has resisted outside control for centuries, has long been considered a likely hiding place for the top two Al Qaeda leaders.

In Karikot, a town a few miles from the heaviest fighting, elders convened an emergency jirga — or tribal council — and accused the army of breaking long-standing agreements for conduct in the region.

At the Rehman Medical Complex in Wana, the main town in South Waziristan, two sisters — Haseena, 10 and Asmeena, 2 — received first aid after being struck by shrapnel. The girls' 12-year-old brother, Din Mohammed, was killed when a shell landed near their house in the village of Kaga Panga.

Bin Laden and al-Zawahri — who also serves as bin Laden's personal physician — have traveled together in the past, and both appeared jointly in videotapes released shortly after the Sept. 11, 2001, attacks on the United States.

In a broadcast on Feb. 24, Al-Zawahri, 52, taunted Bush and threatened more attacks on the United States.

The United States has offered a $25 million reward for information leading to al-Zawahri's capture. On Thursday, the U.S. House of Representatives doubled the reward for bin Laden's capture to $50 million.

Under pressure from Washington, Pakistan has arrested more than 500 Al Qaeda suspects and has turned most over to the United States. The last major capture was that of Khalid Shaikh Mohammed (search), the former Al Qaeda No. 3, who was nabbed on March 1, 2003, near the capital. He is being held at an undisclosed U.S. location.

Afghanistan Nabs Their Own Bad Guys

A spokesman for Afghan President Hamid Karzai (search) said U.S. and Afghan troops have captured "semi-senior" terrorist leaders along the border with Pakistan, as they tightened security along the rugged frontier.

Presidential spokesman Jawed Ludin said it was unclear if those detained had fled the battle in Pakistan, and declined to give any details of who might be in custody.

"Some of the arrests have included semi-senior leadership within the terrorist elements on the Afghan side, possibly with strong links to Al Qaeda," he said.

Fox News' Bret Baier, Mike Emanuel, Greg Kelly and The Associated Press contributed to this report.