The Washington Post had reported that the United States was deploying parts of more than two battalions, and could send as many as 1,000 soldiers from the 101st Airborne Division to the Afghanistan-Pakistan border, beefing up an operation pursuing fugitive Taliban and al Qaeda fighters.
"The number is high. But certainly a large number are being moved," a senior U.S. official told Reuters.
Military officials downplayed the developments but left the door open for further movements.
"Although it's nothing significant right now, that could change any time," said Marine Gen. Peter Pace, vice chairman of the Joint Chiefs of Staff.
He was referring to the work of several hundred troops, including Afghans, Australians, British and soldiers from America's 101st Airborne Division, who other Pentagon officials said were going to sites in Afghanistan along the Pakistani border, in several separate missions aimed at finding hiding enemy fighters and disrupting their operations.
Meanwhile, attackers fired a rocket early Wednesday at the building where U.S. forces searching for al Qaeda members in Pakistan's wild tribal region were sleeping, a local Pakistani official said. The rocket missed and no one was injured.
The United States also has moved Apache helicopters to a U.S. special forces base near the city of Khost, 20 miles from the Pakistan border. U.S. officials believe hundreds of al Qaeda fighters and their Taliban allies are hiding in the area.
The Post said U.S.-led forces on both sides of the Afghan-Pakistan border were acting in part on recent unconfirmed intelligence reports that place al Qaeda leader Osama bin Laden and his top lieutenant in the tribal areas on the Pakistani side of the border.
The Pakistan-based Afghan Islamic Press (AIP) had a similar report Wednesday, saying U.S. forces have launched a fresh operation against Taliban and al Qaeda fighters in the mountains of eastern Afghanistan.
The rocket was fired about 3 a.m. at a vocational training institute in Miram Shah, about 9 miles from the Afghanistan border in rugged northwestern Pakistan, an official in Miram Shah said on condition of anonymity.
Local people said the attackers aimed at the institute but hit an adjacent college building, damaging a wall and windows. No one was hurt because the building was empty, the official said.
It was not known who fired the rocket.
In other developments, CBS News Correspondent Lee Cowan reports that American and Afghan troops have landed in a potentially dangerous position.
U.S. officials say that for the first time, Afghanistan's interim leader Hamid Karzai has ordered an attack on a group of his own Afghan forces.
The target is Padshah Kahn, an Afghan warlord who agreed to talk with CBS News in private Tuesday. He admits he's responsible for a string of attacks on the interim government this month -- but he's also officially a U.S. ally, charged with protecting American special forces in Khost.
That's the same Pakistani border town where allied troops have just come under attack in two separate incidents. The firefights between U.S.-led special forces and suspected al Qaeda terrorists left up to four of the suspects dead, a U.S. general said Tuesday.
In the first of the two attacks, Australian military officials said their special forces shot some attackers Monday after coming under mortar and rocket-propelled grenade fire. "Our soldiers returned fire, killing or wounding two of the terrorists," said Brig. Mike Hannan, a spokesman for the Australian military in Canberra.
In the second attack, Maj. Gen. Franklin L. Hagenbeck said two others were killed before dawn Tuesday. Australian special forces were also involved in that firefight, U.S. officials said.
No allied soldiers were hurt. Hagenbeck said that while the hunt for al Qaeda and Taliban fighters has weakened the enemy, it still had the ability to launch "low-level" terror attacks.
It wasn't clear why the attackers were identified as al Qaeda suspects rather than Taliban.
In recent days, the U.S. has gained a toehold across the border into Pakistan's lawless tribal lands, with a small American force assisting Pakistani troops in their search for fugitives.
But the fresh battles are another indication that alliances the U.S. formed with Afghan forces in December may not be as reliable -- or easy to disarm –- as hoped.
"If we are attacked by any forces," Khan warned Tuesday, "there is going to be trouble."
Just one of Kahn's ammunition caches CBS News found alongside the road contained hundreds of rockets and rocket launchers that haven't been seized.
U.S. military spokesman Maj. Bryan Hilferty conceded that the security situation in eastern Afghanistan had deteriorated because of recent flare-ups of factional fighting, but that wasn't stopping coalition troops from conducting operations.
"Certainly over the last couple weeks it's gotten a little worse in the Khost and Gardez area, but still we are free to move around," Hilferty said.
Hilferty said a 200-man quick reaction force — two infantry companies from the 101st Airborne Division — were flown in by helicopter two hours after Monday's attack and found mortars, grenades and machine-gun ammunition in a sweep of buildings and nearby caves. He said the surviving fighters appeared to be part of a larger group that had fled into surrounding mountains.