Pakistani security forces killed 16 suspected militants and wounded 25 others Sunday in a besieged tribal region — the latest round of a military offensive with no end in sight, officials said.

More than 100 people, most of them militants, have been reported killed in the fighting in the Bajur tribal area in the past five days. The region, which borders Afghanistan, is a suspected hide-out of al-Qaida leader Osama bin Laden and his deputy, Ayman al-Zawahri.

The latest clashes also come amid tension between the U.S. and Pakistan over American incursions aimed at eradicating militants in the Muslim nation's territory.

Security forces used helicopter gunships, fighter jets and heavy artillery to attack suspected militant positions Sunday in the Loi Sam, Rashakai, Tang Khata and Gollokass areas of Bajur, said Iqbal Khattak, a government official who provided the death and wounded tolls.

The government said late last month that it would cease military operations in Bajur for the Muslim holy month of Ramadan, but reserved the right to retaliate against insurgent activities.

Army spokesman Maj. Gen. Athar Abbas said factors including persistent militant mortar attacks and threats to pro-government tribes prompted the military to restart its operation.

"It may take long, but this issue has to be resolved once for all," Abbas said. "It may take a long time. We cannot just hand over this area to the Taliban."

Hundreds of militants were reported killed in Bajur in August in the military offensive, which also was said to have displaced some 300,000 people. The figures have been difficult to confirm independently because of the remote and dangerous nature of the areas involved.

U.S. officials are worried that Pakistan has not done enough to flush out militants from its tribal areas, and that its intelligence agencies might even be secretly aiding insurgents. Al-Qaida and Taliban militants are believed to have found safe havens in the tribal areas from which to plan attacks on U.S. and NATO forces across the border in Afghanistan.

A series of suspected U.S. missile strikes and an American-led ground assault in Pakistani territory in recent days, however, have stirred anger and prompted Pakistan's government to lodge protests.

Although Pakistan has vowed to defend its territorial integrity and publicly denounced the U.S. incursions, top officials have indicated they would prefer to resolve the conflict through diplomatic means.

Pakistani President Asif Ali Zardari, who is visiting Britain, was expected to discuss the cross-border strikes with British Prime Minister Gordon Brown this week.

Meanwhile, Khattak said many Bajur residents who had returned from relief camps because of the Ramadan suspension were again fleeing the tribal region because of renewed fighting.

Many families were taking routes along mountains and gorges to avoid security checkpoints on main roads. Some used donkeys to carry their possessions.

One resident, Abdul Malik, was heading to the Dir area north of Bajur with his wife and three children. He said they were trying to return to the relief camp they'd vacated upon hearing of the Ramadan suspension.

"This is more fierce fighting than before, and we don't know who is killing whom, as no big figure has been killed as yet, only innocent civilians," Malik said.