**Missiles fired by a suspected US drone aircraft have killed at least three militants in north-west Pakistan, security officials say.**The attack targeted a residential building inside the compound of a veterinary hospital in Miranshah, the main town in North Waziristan.
The identities of the militants killed in the attack are not yet known.
North and South Waziristan are known sanctuaries for al-Qaeda and Taliban militants and are often hit by drones.
There have been more than a dozen such strikes this year alone.
Locals say the attacks have destroyed many training camps and compounds. They have also killed dozens of local and foreign militants, officials say.
Security officials told the BBC Urdu Service that three missiles were fired at the building on Sunday.
The dead and six others who were injured in the attack were local militants affiliated to a group led by Hafiz Gul Bahadur, officials said.
The compound of the hospital includes several residential houses for employees, but most of them have left after the area was taken over by the Taliban.
The buildings are now being used by the Taliban, residents say.
The United States has stepped up drone attacks in the region since seven CIA officers died in a suicide bomb attack at a US base across the border in Afghanistan last December.
More than 700 people have died in nearly 80 drone strikes since August 2008.
A surge in such strikes has been ordered by US President Barack Obama.
Pakistan has publicly criticised drone attacks, saying they fuel support for militants, but observers say the authorities privately condone the strikes.
The American military does not routinely confirm drone operations, but analysts say the US is the only force capable of deploying such aircraft in the region.