They were the first known militant casualties in South Waziristan - where Pakistan Taliban head Baitullah Mehsud and al-Qaida figures are believed to be hiding
- since the military started pounding the area with artillery about a week ago. Mehsud is blamed for a series of suicide attacks that have killed more than 100 people since late May.
Although the army has not announced a formal start of full-scale operations in South Waziristan
- an offensive that Washington has been pressing Pakistan to undertake - officials said troops are already occupying strategic positions in the region.
The operation, seen as a test of nuclear-armed Pakistan's resolve against an insurgency that has expanded in the past two years, could be a turning point in its sometimes halfhearted fight against militancy. It also could help the war effort in Afghanistan, because the tribal belt has long harbored militants who launch cross-border attacks.
Jet fighters flattened two abandoned militant-linked seminaries and a training facility Friday in a clear sign that the operation was ramping up.
Two intelligence and army officials, speaking on condition of anonymity because they were not authorized to speak to media, said heavy fighting was under way in the villages of Barwand and Madijan, with about 50 militants killed.
A military statement said 37 extremists were killed when they tried to block the main South Waziristan road near the town of Sarwaki. There was no way to reconcile the differing death tolls due to restrictions on media access to the region.
Meanwhile, artillery fire was pounding militant positions in the Biha valley, in the upper Swat Valley, following an intense operation there Friday night against one of few remaining Taliban strongholds in the region.
"This area is the center of gravity for the terrorists," said Maj. Gen. Sajjad Ghani, who is in control of efforts to clear Taliban from a 3,860-square-mile (10,000-square-kilometer) area in the northern Swat valley.
"As of now, there are only pockets of resistance left. The terrorists are on the run. Command and control is disarray. They are unable to organize an integrated response," he said.
During a military-sponsored trip for journalists to Chuprial, Ghani said 95 percent of the region under his control has been cleared and that most of the resistance the military is facing is in Biha, a short valley that backs into snow-covered mountains that are limiting the Taliban's efforts to flee.
He said about 400 militants have been killed in the area during the six weeks of fighting, but conceded many top commanders have managed to escape, some possibly headed to havens in Afghanistan or the Waziristan tribal areas.
Up to 3,000 militants may be left in the area, but only 500 of them are "hard-core" fighters and the rest are recruits who would return to civilian life once military authority is re-established, Ghani said.
The information from the military could not be independently confirmed because access to large parts of the Swat region is restricted.
Overall, the army says it has killed nearly 1,500 militants since April in Swat.