Pakistan's military said Tuesday it is in the early stages of an operation against the country's Taliban leader in an area considered the deepest stronghold of al-Qaida and other militants.

South Waziristan, in the lawless border region with Afghanistan, has been hit by air raids and military shelling in recent days, but military and government officials insisted Tuesday this was not the formal start of the campaign.

The offensive targeting Pakistani Taliban leader Baitullah Mehsud is eagerly anticipated because it will strike at the heart of the area where militants blamed for attacks both in Pakistan and on Western troops in Afghanistan have become entrenched.

Spokesman Maj. Gen. Athar Abbas told a news conference the military had received orders from the government to begin operations against Mehsud, whose base is in South Waziristan.

"The necessary measures and steps which are part of a preliminary phase of the operation, the preparatory phase of the operation, that has commenced," Abbas told reporters.

But Information Minister Qamar Zaman Kaira stressed that the operation "has not been officially started."

They declined to give more details, saying secrecy was needed to protect the operation.

The reticence may indicate the armed forces are not yet ready for a full-scale battle in the region, a hard-scrabble, mountainous area where well-armed tribes hold sway and the government's influence is minimal.

They may also be talking up the operation before launching it to allow civilians time to flee.

The military is in the final stages of an operation to clear Taliban from the Swat Valley region, another area of Pakistan's volatile northwest. Abbas said the most populated areas were now free of militants.

The government is seeking to capitalize on the relative success of the six-week-old Swat offensive and a decline in sympathy for the Taliban — fueled by a recent wave of terrorist attacks across the country — to open a new front in the tribal zone.

The military action is being welcomed by the United States as a strong stand against militants after years of failed offensives and unsuccessful peace deals rather than confronting Taliban hard-liners directly.

But the weak government is also keenly aware that public support could sour if civilian casualties escalate or the task of resettling more than 2 million refugees displaced by the fighting in Swat is badly handled.

Kaira said the government is prepared to weather a fresh terrorism campaign if necessary to carry out the mission to capture or kill Mehsud, who is blamed for a string of suicide bombings and other attacks in retaliation for the Swat operation. More than 100 people have died in the attacks across Pakistan since late May.

"The risk of lives is there, we have to give sacrifices, we have to pay this price and the nation is ready to give this price to get rid of this menace," he said.

Abbas told reporters there were unconfirmed reports that an al-Qaida-linked Uzbek militant leader, Tahir Yuldash, was injured in a Pakistan air force strike Sunday in the Makeen area of South Waziristan. He gave no further details.

Yuldash is the leader of the Islamic Movement of Uzbekistan and has survived many military operations in the tribal regions bordering Afghanistan after the Sept. 11, 2001 attacks in the United States. His group is widely regarded as having ties to al-Qaida.

The military has struck suspected militant strongholds in South Waziristan and neighboring Bannu with shells and bombs in recent days, and began controlling roads leading in and out of the region. But there has been little sign of large-scale fighting.

South Waziristan has frequently been the site of U.S. missile strikes, the latest one on Sunday.

On Monday, Pakistan military chief Gen. Ashfaq Parvez Kayani denounced terrorists as enemies of the country and Islam, but warned his officers to avoid killing civilians as they widen their operations against the Taliban.

"In the present circumstances ... it is difficult to differentiate between friend and enemy," Kayani told a group of officers. "The problem is that you have to separate black from white ... to avoid collateral damage."