Those detained included foreigners and the local Pashtun tribesmen who have been sheltering them, said Lieutenant General Safdar Husayn, the military commander who is in charge of the sweep.
Husayn said 400 to 500 fighters were believed to still be fighting from within heavily fortified compounds, using mortars, AK-47s, rockets and hand-grenades in a face-off with troops.
"These people have been here for a long, long time. They are extremely professional fighters," he said. "They have tremendous patience before they open fire."
"They are taking us from every direction whenever our troops have moved in and we are not knowing if the locals are with us," he added. "With an undefined target like this, it is practically chasing shadows."
The military showed journalists 40 prisoners, all blindfolded and with their hands tied, who were sitting under heavy guard in the back of a military truck in Wana, the main town in the tribal South Waziristan region, where the battle was raging.
The army also displayed the body of one suspected fighter wrapped in a white blanket.
Husayn said troops were convinced the compounds held a "high-value" target, but he said they had no confirmation the man was al-Zawahiri.
Bin Laden 'fine'
Meanwhile, al-Qaida leader Usama bin Ladin and al-Zawahiri, are reported to be safe.
"Muslims of the world – don't worry about them, these two guests are fine", a Taliban spokesman Abd Al-Samad, told AP by telephone.
At least 43 people have already been killed in the assault which began early last week, in South Waziristan – a forbidding tribal region, with several mud fortresses, near the border with Afghanistan.
Tribesman near the mountainous
area where offensive is underway
"The operation is on", Pakistani army spokesman Major General Shaukat Sultan said on Saturday. He reported no arrests of any senior al-Qaida member, backing the Taliban spokesman's comments.
On Friday, Sultan said the Pakistani forces were joined by "a dozen or so" American intelligence agents in the ongoing offensive. US satellites, predator drones and other surveillance equipment hovered overhead.
Mix of fighters
An estimated 300 to 400 fighters – a mix of foreigners and Pakistani tribesmen – were facing off against the military in several villages including Kaloosha, Azam Warsak and Shin Warsak, according to Sultan.
Sultan said authorities' intelligence assessment was that a high-level fugitive was among the fighters, but that he had not been seen and it was unclear whether it was al-Zawahiri.
"Muslims of the world – don't worry about them, these two guests are fine"
"The type of resistance, the type of preparation of their defensive positions, the hardened fortresses they have made means we can assume that there could probably be some high-value target there," Sultan said.
He backed off claims by four senior Pakistani officials that captured fighters had revealed that al-Zawahiri was among them, and possibly wounded.
"So far, whatever people we have apprehended, we have not got confirmation from them," he said, but added that he could not share such intelligence anyway.
Rice said reports of arrest of
al-Zawahiri could not be confirmed
The semi-autonomous region, which has resisted outside control for centuries, has long been considered a likely hiding place for the top two al-Qaida leaders - but there was no indication bin Ladin was with al-Zawahiri, a 52-year-old Egyptian surgeon.
US President George Bush's national security adviser, Condoleezza Rice, told CNN on Friday a "fierce battle was raging", but the US did not have any independent confirmation that al-Zawahiri was surrounded.
The assault began on Tuesday with raids on the homes of tribesmen wanted for sheltering al-Qaida fugitives, erupting into the bloodiest battle involving Pakistani forces since they were deployed to the area two years ago.
At least 15 troops were killed on Tuesday and another 13 are still missing. Other estimates put the military toll at about 30.
Intermittent firing was continuing late on Friday, Sultan said. He refused to speculate how long the operation would last.
"We were eating lunch and all of a sudden the shelling began and it hit our courtyard ... "I loved my brother a lot. What did we do to deserve this?"
Nearly 30,000 civilians, some wounded and others carrying their meagrepossessions – clothes, carpets, pots and pan, fled the battle zone. Many said they knew nothing about al-Qaida fighters in their midst, and expressed outrage at the military assault.
In Karikot, a town a few miles from a few miles from the heaviest fighting, elders convened an emergency jirga - or tribal council - and accused the army of breaking long-standing agreements for conduct in the region.
At the Rahman Medical Complex in Wana, the main town in South Waziristan, two sisters - Hasina, 10 and Asmina, 2 - received first aid after being struck by shrapnel.
The girls' 12-year-old brother, Din Muhammad, was killed when a shell landed near their house in the village of Kaga Panga.
"We were eating lunch and all of a sudden the shelling began and it hit our courtyard," Hasina said, her face bandaged. "I loved my brother a lot. What did we do to deserve this?"
Pakistani tribal guards at the
Waziristan border region
Other civilians who fled to Wana - where there was no bloodshed - said they saw jet fighters and heard heavy gunfire through the night as fighting spread on Friday. Residents reported seeing scores of army trucks carrying troops and weapons from Wana to the target areas.
Under pressure from Washington, Pakistan has sent 70,000 troops into the region since the 11 September 2001 attacks. This week's operation has been by far the bloodiest.
Jordanian and British special forces arrived in Afghanistan to join the operations, according to airport officials in Kabul. About a dozen Americans are also involved in intelligence gathering, but US officials were quick to deny they were actively involved in the fighting.
Authorities hoped to wrap up the operation by Sunday afternoon, Interior Minister Faisal Salah Hayyat said.