If verified, it apparently would be the first time a pilotless aircraft was brought down over Pakistan and likely would add to tensions between Washington and Islamabad over recent American cross-border incursions into the country's lawless tribal regions.
The three officials said the aircraft was hit at the village of Jalal Khel in South Waziristan after circling the area for several hours. Wreckage was strewn on the ground, they said, speaking on condition of anonymity because they were not authorized to brief the media.
A U.S. military spokesman in Afghanistan, Capt. Christian Patterson, said officials were looking into the claim.
The report came a day after intelligence officers said two U.S. helicopters crossed a mile into Pakistan late Sunday over North Waziristan, but flew off after Pakistani troops and tribesmen opened fire. The Pentagon denied any incursion by U.S. helicopters.
While causing widespread anger among Pakistanis, the apparent raids by U.S. forces, including missile strikes and a ground assault, have underlined Washington's concerns that the government is unwilling or incapable of rooting out the Taliban and other extremists on the border.
Pakistani President Asif Ali Zardari was expected to discuss the cross-border attacks with U.S. President George W. Bush on Tuesday on the sidelines of the U.N. General Assembly in New York.
The U.S. is known to operate drones in neighboring Afghanistan that are sometimes used to conduct surveillance of suspected militant hideouts inside Pakistan and occasionally launch missile attacks on the havens. Washington generally does not acknowledge the strikes, which Pakistani officials say often miss their targets and fuel support for the militants.
South Waziristan and other tribal areas in Pakistan's northwest are a haven for al Qaeda and Taliban militants who cross into Afghanistan to attack American and NATO troops as well as for Pakistani extremists who are striking targets in Pakistan.
Militants with roots in the border region are suspected in Saturday's truck bombing at the Marriott hotel in Islamabad. The attack killed 53 people, among them the Czech ambassador and two U.S. Defense Department employees, and wounded about 270.
Washington is concerned that the Pakistani government is unwilling or incapable of rooting out extremists and wants Islamabad to do more to combat the problem. Pakistan says it has deployed tens of thousands of soldiers to the area and they regularly battle insurgents.
In the latest fighting, troops backed by helicopter gunships and artilleryin the Kohat region since Monday, an army spokesman, Maj. Murad Khan, said. One solider also died, he said. Khan said the military regained control of a mountain road tunnel seized by insurgents several days ago.
In the nearby Bajur tribal region, security forces killed at least 10 militants Tuesday in the latest round of a major offensive there, government official Iqbal Khattak said.
Pakistan's army spokesman Maj. Gen. Athar Abbas has said Bajur had turned into a "mega-sanctuary" for militants and the military was determined to flush them out.
The surge in violence is the biggest challenge facing Pakistan's new civilian government, which is having to balance Washington's demands against deep unhappiness among his people over the alliance with the United States.
In a speech to Muslim scholars late Tuesday, Prime Minister Yousuf Raza Gilani said terrorists are "enemies of Islam with no faith" and vowed to get tough on militants sheltering in the border region.
"We will not allow them to challenge the writ of the government and create a law of the jungle and a life of the stone age," he told a gathering of Muslim scholars in the capital, Islamabad.
Meanwhile, at least six people - including a 12-year-old boy - were killed and a bank set afire Tuesday during rioting in Mangora in the northwestern Swat Valley, police and a hospital official said.
It was unclear how the people died, but police said officers fired warning shots trying to control a mob that was protesting the lack of electricity and natural gas. Police officer Mohibullah Khan said militants bombed the local power station and gas pipeline last week.
The bombing of the Marriott continued to affect operations of diplomatic missions, aid groups and other organizations.
British Airways said Tuesday it "indefinitely" suspended flights to Pakistan "in light of the current security situation." A British Embassy spokesman, Aidan Liddle, said a company that runs four visa application centers for the embassy closed them pending a security review.