Pakistan's army chief has appealed to members of a major tribe linked to the Taliban to support an offensive against the insurgents, a move aimed at further isolating an enemy blamed for a wave of bloodshed in the nuclear-armed, U.S.-allied nation.

The Pakistani military's operation against the Pakistani Taliban in South Waziristan is considered its most critical fight against Islamist extremists threatening its stability, and its strategy involves convincing other warlords and tribes in the region to stand aside during the fight, even if they are involved in anti-U.S. activities in Afghanistan.

Army chief Gen. Ashfaq Parvez Kayani's letter — dropped as leaflets from the air in South Waziristan — was addressed to the Mehsud tribe, whose members populate the top ranks of the Pakistani Taliban, a group bent on overthrowing the central government.

The Mehsuds are a huge tribe with several subsections. Many members live far from the tribal badlands, and are involved in a range of professions and businesses. The tribe dominates Pakistan's transport sector.

The Pakistani Taliban chief is Hakimullah Mehsud, a main target of the offensive.

The Taliban have killed hundreds of tribal elders throughout the Afghan border region to undermine the age-old administrative system there and solidify control. Loyalties run deep among tribesmen, and codes of honor prevent them from informing on each other, even if one is suspected of anti-government activity.

Kayani described the Mehsuds as courageous, loyal Pakistanis, urging them to "rise collectively" against militants in their midst.

"The ongoing operation by the Pakistani army is not aimed at the patriotic Mehsud tribes," he wrote, according to a version posted on the army's Web site. "Instead the target is for the good-riddance of the Mehsud tribes from the cruel clutches of terrorist elements who have ruined the law and order and peace of this area."

The army also has struck deals to keep two powerful, anti-U.S. tribal chiefs from joining the battle.

The deals increase the chances of an army victory, but indicate that the 4-day-old assault may have less effect than the U.S. wants on a spreading insurgency across the border in Afghanistan.

Under the terms agreed to about three weeks ago, Maulvi Nazir and Hafiz Gul Bahadur will stay out of the current fight in parts of South Waziristan controlled by the Pakistani Taliban. They will also allow the army to move through their own lands unimpeded, giving the military additional fronts from which to attack the Taliban.

In exchange, the army will ease patrols and bombings in the lands controlled in North and South Waziristan by Nazir and Bahadur, two Pakistani intelligence officials based in the region told The Associated Press on condition of anonymity because revealing their identities would compromise their work.

Western officials say South Waziristan is also a major sanctuary and training ground for al-Qaida operatives. The mountain-studded region has been under near-total militant control for years and is considered a likely hiding place for Osama bin Laden.

U.S. officials are watching the offensive closely with the hope that the Pakistani army will not pull back after the initial onslaught, and will eventually widen the offensive beyond the faction loyal to Taliban leader Hakimullah Mehsud to cover other militant factions and the more forbidding ground of North Waziristan.

The army's offensive in South Waziristan pits some 30,000 troops against 11,500 militants. The army has conducted three previous offensives in South Waziristan since 2004, all unsuccessful.

The army said Monday that troops backed by aerial bombing were steadily advancing on three fronts into the region and meeting stiff resistance in places. It said 78 militants and nine soldiers were killed over the last three days.

It is nearly impossible to verify independently the information because access to the region is blocked.

As many as 150,000 civilians — possibly more — have left South Waziristan in recent months. Authorities say that up to 200,000 people may flee in the coming weeks, but don't expect to have to house them in camps because most have relatives in the region.