US drone attacks up till Friday, have killed 21 suspected militants in north-western Pakistan, intelligence officials said.

A drone fired two missiles at a vehicle in North Waziristan, a tribal district along the border with Afghanistan know as hideout for Taliban and al-Qaeda insurgents, killing six suspected militants.

'This was the second attack in the day and it killed six militants,' said a local intelligence official on condition of anonymity.

Earlier, five suspected militants were killed and seven were seriously wounded in a predawn airstrike at a compound used by gunmen in the Spalga area near Miransha, the main town in North Waziristan. The compound was destroyed in the attack.

A strike by an unmanned US drone killed nine militants last week in the same area, where fighters from the Haqqani network, an Afghan group allied with the Taliban, are active.

The United States appears to have resumed controversial drone attacks after airstrikes in November on a Pakistani army border post killed 24 soldiers, raising tensions with Pakistan.