A raid by a US drone in northwest Pakistan has killed at least 12 suspected opposition fighters, Pakistani officials have said.

The attack took place on Sunday in the Shaktoi area of South Waziristan, close to the Afghanistan border.

"The target was a militant compound," a senior military official said of the raid, which occurred about 40km southeast of Miranshah, the primary town in North Waziristan.

Another official added: "The drones are apparently tracking and targeting Pakistani Taliban chief Hakimullah Mehsud, whose presence is frequently reported in the area."

Conflicting reports have emerged over the past few days of Mehsud's death.

On Saturday, the Pakistani Taliban released an audio recording in which a voice purporting to be that of Mehsud said that he had not been killed in a US bomb attack last Thursday.

About 40 opposition fighters are said to have been killed by drone strikes since last Thursday, as Washington steps up its campaign to counter the Taliban and al-Qaeda in Pakistan.

The latest attack is the 10th US drone strike this year. The use of the pilotless aircraft has been criticised by Pakistani officials for causing civilian casualties, as well as for breaching the country's sovereignty.

Barack Obama, the US president, has put Pakistan at the centre of his policy to target the Taliban and al-Qaeda, seeing lawless tribal areas of western Pakistan as a safe haven for such fighters.