US drone missiles have struck a building in North Waziristan, in Pakistan's north-west tribal belt, killing five people.

Pakistani government officials have not revealed the identities of the dead, but it is probable the targets were members of rebel groups.

North Waziristan, which is on Pakistan's border with Afghanistan, is used as a sanctuary by al-Qaeda and the Taliban.

The US has recently stepped up its drone attacks as the CIA hunts a bomber who killed seven CIA employees late last year in the border area.