Pakistan’s army, in the midst of a major new offensive against Taliban militants, has struck deals to keep two powerful, anti-U.S. tribal chiefs from joining the battle against the government, officials said on Monday.

The deals increase the chances of an army victory against Pakistan’s internal enemy No. 1, but indicate that the 3-day-old assault into the Taliban’s strongholds in South Waziristan 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, Taliban renegades 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 by Nazir and Bahadur, two Pakistani intelligence officials based in the region told The Associated Press on condition of anonymity.

An army spokesman described the deal as an “understanding” with the men that they would stay neutral. The agreements underscore Pakistan’s past practice of targeting only militant groups that attack the government or its forces inside Pakistan.

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.

The United States has responded cautiously to the initial Pakistani strategy, publicly welcoming the offensive but saying little about the specific choice of targets.

“We have a shared goal here, and the shared goal is fighting violent extremism,” State Department spokesman Ian Kelly said Monday.

Mr. Kelly said he was unaware of an agreement to keep some militant factions out of the fight for now, but other U.S. officials said the strategy is not surprising or necessarily worrisome.

Because the faction loyal to Taliban leader Hakimullah Mehsud poses the most direct threat to the Pakistani government and army, it is the logical first target, U.S. officials briefed on the offensive said.

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 to cover other militant factions and the more forbidding ground of North Waziristan.

The army’s offensive in South Waziristan is pitting some 30,000 troops against 11,500 militants belonging to the Pakistani Taliban, an umbrella grouping of the country’s main militant factions blamed for 80 percent of the attacks in this nation over the last three years.

The Taliban have claimed responsibility for a surge in strikes over the past two weeks that has killed more than 170 people. The attacks have included a 22-hour siege of the army headquarters and a bombing of the U.N. building in the capital, Islamabad.

Pakistani security analysts said the army had little choice but to cut deals with rival Taliban factions to have a chance of success. The campaign will likely be far tougher than in the Swat Valley, a northwest region where government troops overpowered insurgents this year. The army has conducted three previous offensives in South Waziristan since 2004, all unsuccessful.

“If the army opens up multiple fronts, they will be deluged,” said Khalid Aziz, a former top administrator in the northwest. “It’s like having a patient suffering from multiple diseases — you tend to treat those that are life-threatening first.”

The army is setting its sights on Hakimullah Mehsud, who became leader of the Pakistani Taliban after its former chief, Baitullah Mehsud, was killed in a U.S. missile strike in August.

The army said on Monday that troops backed by aerial bombing were steadily advancing on three fronts into the region and meeting stiff resistance in places. It said that over 70 militants and nine soldiers were killed over the last three days.

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