ISLAMABAD - Pakistan's military said Tuesday that it is in the early stages of an operation targeting the country's Taliban leader Baitullah Mehsud in a key stronghold of al-Qaida and other militants.

The military has shelled and launched air raids in South Waziristan, which borders Afghanistan, in recent days. Convoys of military trucks carrying tanks and heavy artillery were seen Tuesday in the nearby towns of Dera Ismail Khan and Tank. Intelligence officials said they were part of the buildup for the operation against Mehsud.

But there has been little sign so far of large-scale fighting, and military and government officials insisted Tuesday the recent shelling did not mark the formal start of the campaign.

The offensive is eagerly anticipated, not least by Washington. Militants entrenched in the region are blamed for attacks both in Pakistan and on Western troops in Afghanistan. South Waziristan has frequently been the site of U.S. missile strikes targeting militant leaders, the latest one on Sunday.

The buildup comes as the army enters the final stages of a major operation against Taliban in the northwestern Swat Valley, which has triggered a wave of retaliatory suicide attacks by militants across Pakistan.

Army 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, citing operational secrecy.

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 Swat operation, launched six weeks ago, has displaced more than 2 million people.

Abbas said most populated areas of Swat were now free of militants.

The government is seeking to capitalize on the relative success of that offensive and waning public sympathy for the Taliban to open a new front in the tribal zone. The wave of terrorist attacks, including deadly bombings against security forces, a mosque and an upscale hotel housing aid workers, have caused outrage.

The army shelled suspected militant hideouts in three villages in South Waziristan on Tuesday in response to attacks on two military checkpoints, two intelligence officials told The Associated Press. Two other officials said helicopter gunships targeted suspected Mehsud hideouts in various areas of South Waziristan. One official called them "surgical strikes" ahead of the main operation.

The officials spoke on condition of anonymity because they were not authorized to disclose information to the media.

The United States has welcomed Pakistan's recent military action as a strong stand against militants after years of failed offensives and unsuccessful peace deals.

But Pakistan's weak government is also keenly aware that public support could sour if civilian casualties escalate or the task of resettling those 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.

Mehsud, who is also accused of masterminding the 2007 assassination of former Prime Minister Benazir Bhutto - the wife of current President Asif Ali Zardari - is blamed for the string of suicide bombings and other attacks carried out 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," Kaira 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.

Associated Press writers Ishtiaq Mahsud in Dera Ismail Khan, and Munir Ahmad and Zarar Khan in Islamabad contributed to this report.

AP-WS-06-16-09 1025EDT