Anti-Taliban troops said they clashed Wednesday with fighters loyal to Usama bin Laden's Al Qaeda network near their hideouts in the towering mountains along the Pakistan border as they conducted their search for the alleged terror mastermind.

Early Wednesday, U.S. B-52s passed over the Tora Bora cave complex, the target of intensive U.S. bombing for days. Smoke could be seen rising from the mountains, and an anti-Taliban commander reached by phone said part of the complex had been captured and some Arabs had been killed.

On Tuesday, hundreds of fighters piled into trucks and headed to the White Mountains south of Jalalabad to join the hunt for bin Laden. Provincial security chief Hazrat Ali said he was assembling a force of about 3,000 more men.

Ali said Tuesday that a patrol of about a dozen men clashed briefly with a group of Al Qaeda fighters, who abandoned a tank and scurried to higher ground. There were no casualties, Ali said.

As many as 1,200 Al Qaeda fighters could be hiding in the rugged mountains, outside Jalalabad, said Mohammed Zaman, defense chief in Nangarhar province. They appear to be fleeing to higher altitudes as they abandon the Tora Bora complex. Ali said the Al Qaeda forces have split into groups as small as 10 men.

"This fight has just begun," Gen. Richard Myers, chairman of the U.S. Joint Chiefs of Staff, said in Washington.

A U.S. soldier was wounded Tuesday during the fighting around Kandahar, the Taliban militia's southern stronghold, defense officials in Washington said.

The soldier was shot in the upper chest under the collarbone, but his injuries were not life-threatening, said the officials, who spoke on condition of anonymity. The soldier was working with one of the anti-Taliban groups surrounding Kandahar.

Zaman, the Nangarhar defense chief, claimed an airstrike late Monday killed bin Laden's finance chief, known variously as Ali Mahmoud or Sheik Saiid, and injured bin Laden's chief lieutenant, Ayman al-Zawahri. U.S. officials were skeptical of the claim.

Sources in Egypt close to Islamic militants in Afghanistan said Tuesday the wife and three daughters of al-Zawahri were killed in an airstrike on Kandahar on Sunday. The sources, speaking on condition of anonymity, said several other relatives of Arabs serving in Al Qaeda died in the same airstrike.

In Washington, a U.S. official, also speaking on condition of anonymity, said the United States has credible reports that members of al-Zawahri's immediate family were killed in a U.S. airstrike.

Defense Secretary Donald H. Rumsfeld would not discuss whether American ground troops were actively involved in the hunt for Al Qaeda in the Jalalabad area. But he said the Americans "have been actively encouraging Afghan elements to seek out" Al Qaeda leaders.

Gen. Tommy Franks, commander of U.S. forces in the Afghan conflict, has confirmed that the search for bin Laden, sought in the Sept. 11 terrorist attacks in the United States, has focused on the mountains south of Jalalabad and around Kandahar.

Kandahar Still Holding Out, Marines Probe Deep Into Desert

Marine reconnaissance units out of a U.S. base outside Kandahar have begun probing deep in the desert, moving in off-road vehicles and Humvees.

Capt. David Romley, a spokesman for the Marines' Task Force 58 at the base, did not specify the teams' mission, saying only that they were "looking for threats. ... Any threat is going to be a target."

The more than 1,000 Marines at the base, set up at an airfield just over a week ago, have not gotten involved in fighting as anti-Taliban tribesman advance from three directions on Kandahar, the last city under Taliban control.

A coalition official, speaking in Pakistan on condition of anonymity, said the Marines were "obviously not a big enough force to take Kandahar," but would join efforts to prevent Taliban escaping.

The Taliban have vowed to defend the city, where their movement was organized nearly a decade ago.

Tribesmen loyal to former Kandahar governor Gul Agha fought their way onto the airport compound a few miles south of the city Tuesday but were pushed back two miles by about 500 Al Qaeda fighters, according to Abdul Jabbar, a tribal spokesman in Pakistan.

Jabbar said U.S. special forces were calling in airstrikes in support of Agha's fighters. The Taliban admitted the U.S. bombing was taking its toll.

If not for the airstrikes, "people like Gul Agha wouldn't be a problem for us," said Mullah Qasim, a Taliban commander south of Kandahar. "We could push him back not in days, but hours."

Another tribal force under Hamid Karzai — who was appointed interim prime minister by the delegates in Bonn, Germany on Wednesday — is pushing toward Kandahar from the north and met its first resistance Tuesday, according to a senior U.S. official.

The official, speaking in Pakistan on condition of anonymity, said Karzai's men battled Taliban defenders at a bridge 10 miles north of Kandahar. It was unclear if the Taliban were still holding the bridge.

The Associated Press contributed to this report.