The strike took place in North Waziristan just around three miles (five kilometers) from the Afghan border, the officials said, speaking on condition of anonymity because they were not allowed to speak to the media.
A volley of missiles landed on a house, killing six people who were either inside or arriving there, the officials said.
The identities of the victims were not immediately known.
The United States has carried out at least 90 attacks on suspected militant targets this year in northwestern Pakistan, close to double the number in 2009. They have been credited with killing scores of insurgents, though there are also accounts of civilian casualties.
Most of the strikes this year have been in North Waziristan, which is home to thousands of Al-Qaeda and Taleban militants as well as insurgents who use the area as a staging ground for attacks against US and NATO forces in Afghanistan.
The Pakistani army, which has battled militants in other strongholds in the northwest over the last two years, does not aggressively patrol the area or attack insurgents there.
Independent reporting on the strikes is nearly impossible because the areas they fall in are mostly under militant control and out of bound to journalists, local or foreign.
The United States does not officially acknowledge firing the missiles.
