Pakistani forces backed by helicopters and artillery leveled three houses and detained at least 20 people Tuesday, sweeping through villages in a remote border region where Usama bin Laden and Al Qaeda militants are believed to be hiding.

The searches near the town of Wana, just a few miles from the border with Afghanistan, began after dawn, as paramilitary and army troops moved into areas where the fugitives are believed to have taken refuge among local tribes.

Using artillery, troops leveled homes belonging to three tribesmen who were allegedly sheltering fugitives.

Three Arab women were among those detained, though it was not immediately clear if they were under arrest.

"They were given an enough time," a government official supervising the operation told The Associated Press on condition of anonymity. "We launched the operation when they failed to hand the foreign terrorists over."

People in Wana reported hearing explosions and gunshots throughout the morning.

"We have heard 25 to 30 explosions. The shooting started in the morning and it's continuing," said Shahzad Wazir, a resident in Wana.

The operation, which included more than a dozen helicopter gunships, began in the village of Zarkai, a village in Pakistan's strategic South Waziristan (search) tribal region. It is located about 190 miles west of Pakistan's capital, Islamabad.

Soon, two other villages were also under siege: Kaloosha and Azam Warsak. Both are west of Wana.

Authorities have been talking for days about launching the operation, saying it would go door-to-door if tribal elders did not voluntarily hand over any terror suspects.

The fact the operation was announced in advance suggested that officials saw little chance of surprising bin Laden or other senior Al Qaeda men, but the maneuvers could be designed to make the area less hospitable and force the suspects to flee into Afghanistan, where the Americans lead an 11,000-strong military force and can operate more freely.

The Pakistani government had set Feb. 20 as the deadline for tribal elders to hand over Al Qaeda fugitives and their supporters. So far, about 58 suspects have been turned over, though another 38 are still being sought, officials say.

In recent days, Pakistan stepped up security in the tribal areas, said Mohammed Azam Khan, a local official.

Authorities hope the sweep will yield clues about bin Laden, the Al Qaeda leader. Intelligence officials have long believed that bin Laden is hiding in the rugged mountains between Pakistan and Afghanistan, though there has been no hard evidence of his whereabouts for nearly two years.

The operation comes weeks after CIA director George Tenet is believed to have made a secret trip to Pakistan to discuss the hunt for the Saudi fugitive as well as ways to fight nuclear proliferation.

Pakistan denies that any American troops are involved in operations on its soil, though local residents have in the past said they have seen what they believed to be U.S. special forces in the region.

Pakistan's government has limited authority in the tribal lands, but has been expanding its role under U.S. pressure to crack down on terrorism since the Sept. 11 attacks.

The operation is the fourth against Al Qaeda and Taliban fugitives along the border since Pakistan became an ally of the United States following the terror attacks in Washington and New York.

More than 500 suspected Al Qaeda and Taliban fugitives have been captured, including key figures in bin Laden's terrorist network. Most have been turned over to U.S. authorities.

Foreign Minister Khursheed Kasuri said Monday that any top Al Qaeda fugitives wanted in the United States would be handed over. However, President Gen. Pervez Musharraf has assured tribal elders that suspects who turn over their weapons and surrender would not be extradited.