Residents fleeing a 6-day-old Pakistani army offensive in a Taliban stronghold along the Afghan border reported Thursday that the insurgents are digging in for a fight and travel the roads freely.

Tired and dusty refugees arriving in this northwestern town Thursday from different parts of South Waziristan reported intense army bombing by jets and helicopters but said they had seen no ground troops.

The accounts by a dozen refugees to Associated Press reporters are a sign of just how much fighting remains before the military can even hope to clear the area, which in recent years has become a major global hub for Al Qaeda and other extremist groups who carry out attacks against U.S. troops in Adghanistan.

The militants were believed to control roughly 1,275 square miles of territory before the offensive began. That portion covers about half of South Waziristan, which itself is slightly larger than Delaware.

The military say its troops are progressing steadily and retaking land on three fronts. But officers have made it clear that the campaign will be long and bloody and acknowledged resistance is tough.

As the army presses into their heartland, the militants are trying to bring the war to the rest of Pakistan.

Over the last 20 days, they have killed more than 170 people in a series of suicide bombings and raids on Western, civilian and security-force targets across the country.

In the latest attack, suspected insurgents on a motorbike shot and killed a senior army officer and a soldier Thursday in a residential part of the capital, Islamabad. The slain officer, Ahmed Moinuddin, was on leave from his job as deputy commander of the U.N. peacekeeping mission in Sudan.

The attack came despite ramped-up security nationwide. It was believed to be the first targeted killing of an army officer in the capital, a sign of evolving militant strategies.

The United Nations says 110,000 people have fled South Waziristan in recent months as speculation rose of an army offensive, about 30,000 of them in the last few days. Most are staying with relatives or in rented homes in Dera Ismail Khan and nearby districts.

New arrivals said the Taliban were preparing for a fight.

"We saw no ground forces on the way, nothing except helicopters and airplanes. But we saw a lot of Taliban movement," said Awal Jan, a refugee from the town of Sarwakai. "They were roaming around in their vehicles and digging trenches in the mountains."

Pakistan is under intense pressure to eliminate Islamist militant groups sheltering in its northwest that also attack U.S. and NATO troops in Afghanistan. The military has battled them in various districts, losing hundreds of soldiers, but questions remain about its overall strategic commitment to the fight.

The army has previously moved into South Waziristan three times since 2004. Each time it has suffered high casualties and signed peace deals that left insurgents with effective control of the region. Western officials say Al Qaeda now uses it and neighboring North Waziristan as an operations and training base.

One refugee said Taliban fighters had told villagers they must join them or flee.

"They said, 'If you want to side with us, you may. If you are scared of death, them leave immediately,'" said Habibullah, who gave only a single name.

Maadi Shah, his wife and five children walked for a day to escape.

"Earlier there was aerial bombing once a day, but now it is happening countless times," he said. "We saw the Taliban shifting to the mountains toward Makeen (the main town). They are well-entrenched there," said Shah, who stopped talking after a man warned him of possible Taliban retaliation for meeting reporters.

The current offensive pits 28,000 troops against some 12,000 militants, 1,000 of them believed to foreign fighters, mostly Chechen and Arabs. They are fighting in an unforgiving landscape of hulking mountains, rock-strewn valleys and sparse vegetation.

A military statement Thursday reported two more soldiers were killed, bringing the army's death toll to 18, and that 24 more militants were slain, bringing their death toll to 129. Reporters are blocked from entering the region, meaning verifying information is all but impossible.

Authorities say they are not expecting a major humanitarian crisis like the one triggered by an offensive in the northwestern Swat Valley earlier this year. Still, many refugees have complained of receiving little or no government assistance.

In Paharpur town, some 30 miles outside Dera Ismail Khan, police clubbed refugees swarming an aid distribution center run by Pakistani authorities. The lines were long, and some refugees tried to climb a wall to get inside. Several people were injured, one with a bloodied head.

"We came here for bread, but the police beat us up," said Rahmatullah Mehsud. "There, the Taliban were messing with things and the army was showering bombs. Here, we have to bear the clubs."

Aid administrator Javed Shaikh said there was plenty of food, but that the refugees were "impatient."