Officials said Friday's action did not represent the start of a full-scale operation in the tribal belt along the border with Afghanistan, but that most troops were now in place for when the orders came.

The coming operation in South Waziristan, along with one winding down in the northwestern Swat Valley, could be a turning point in Pakistan's yearslong and sometimes halfhearted fight against militancy.

It could also help the war effort in Afghanistan, because the tribal belt is believed to house key bases of al-Qaida and Taliban militants accused of launching attacks on Western and government forces in Afghanistan.

Washington strongly supports the operations, which are seen as a test of nuclear-armed Pakistan's resolve against an insurgency that has expanded in the past two years.

The Swat offensive has been generally welcomed in Pakistan, but public opinion could quickly turn if the government fails to effectively help more than 2 million people displaced from their homes by the fighting, or if civilian casualties mount.

South Waziristan government official Nematullah Khan said on Friday ground troops had started taking up positions around strongholds of Pakistani Taliban leader Baitullah Mehsud, who is blamed for a series of suicide attacks in Pakistan that have killed more than 100 people since late May.

'Troops have entered Mehsud's areas' for the first time, Mr Khan told reporter. -- AP