The U.S. is dispatching up to 1,000 troops from the Army's 101st Airborne Division to the Afghan-Pakistani border to join coalition forces preparing for a new offensive against Al Qaeda and Taliban forces. 

The Americans will join an existing force of Afghan, Australian, British and Canadian troops that is expected to launch a series of military strikes designed to flush out and eliminate what some fear is a regrouping of enemy forces in the remote and lawless border frontier. 

The buildup, part of the ongoing Mountain Lion operation, comes amid increasing signs of Al Qaeda and Taliban activity in the area. 

Intelligence officials have said small groups of enemy forces, ranging in number from a handful to a couple of dozen, have been seen and are believed to be part of a larger group hiding in the mountains. 

On a search mission Monday night and Tuesday morning, Australian forces were attacked by a group of suspected Al Qaeda fighters, and got into a battle was believed to have killed four enemy fighters. 

A rocket was fired about 3 a.m. Wednesday at a vocational training institute in Miranshah, about nine miles from the Afghanistan border inside northwestern Pakistan, an official in Miranshah said. 

Local officials said the attack was aimed at U.S. forces, but some officials were disputing that report. At the U.S. Central Command in Florida, Air Force Lt. Col. Martin Compton said officials were unaware of the incident and that he had no information that American military were in the building. 

CIA and other paramilitary forces were said to be actively engaged in the area, however, and may have been a target of the attack. 

U.S.-led forces have been focusing heavily on the eastern part of Afghanistan since Operation Anaconda. That campaign in the first two weeks of March, the biggest ground operation of the war, sought to flush fighters out of a 60-square-mile area in the Shah-e-Kot valley near Gardez. 

Since that ended, commanders have continued to send teams and patrols through provinces along the border to find fighters and weapons caches, an effort expanded in April with the arrival of some 1,700 British Royal Marines. 

Enemy forces have been on the move for months, slipping back and forth over the mountainous border into Pakistani tribal areas where they have supporters, Afghan and U.S. officials have said. But they have moved in smaller numbers, leading American commanders to believe future clashes would be consist of lightning raids. 

Both U.S. and Pakistani officials have said in recent days that a small number of U.S. troops have been put on the Pakistan side to support Pakistani troops with communications and intelligence. 

Officials continue to say they have no specific knowledge that Usama bin Laden or any other top Al Qaeda leaders are holed up with the enemy fighters in the Pakistani border areas. But intelligence reports have repeatedly noted that bin Laden is alive and in the region, U.S. officials said. 

The troops will take part in periodic, intensified sweeps through the border areas in addition to military operations focused entirely in Pakistan. But the fighting was not expected to rise to the level of Operation Anaconda, where groups of hundreds of enemy troops were targeted. 

Canadian officials say their Light Infantry forces have not been sent out from Bagram as of yet. U.S. officials say the center of gravity of military operations in Afghanistan has over the past several weeks shifted from Kandahar to Bagram, although forces will remain in Kandahar. Facilities at Bagram are being upgraded. 

Fox News' Bret Baier, Greg Palkot and the Associated Press contributed to this report.