Suspected U.S. missiles struck a vehicle in a militant stronghold on Pakistan's side of the border with Afghanistan on Monday, killing six people, Pakistani intelligence officials said.
The attack in the North Waziristan tribal region came in the final days of a year that has witnessed an unprecedented number of such drone-fired strikes on Pakistani soil, part of a ramped-up U.S. campaign to take out al-Qaida and Taliban fighters seeking sanctuary outside Afghanistan.
At least 110 such missile strikes have been launched this year — more than doubling last year's total. Nearly all have landed in North Waziristan, a region that hosts several militant groups battling U.S. and NATO troops in Afghanistan, including the feared Haqqani network.
The four missiles fired Monday struck the vehicle in the Shera Tala village of North Waziristan. Shera Tala lies in Mir Ali district, where militants are heavily concentrated. The identities of the six dead were not immediately certain.
The two intelligence officials spoke on condition of anonymity because they were not authorized to speak to media on the record.
Pakistan officially protests the strikes, saying they violate its sovereignty and anger tribesmen whose support it needs to fend off extremists. There is widespread belief among tribal residents that the attacks kill many innocent people, though the numbers are difficult to prove.
U.S. officials rarely discuss the covert, CIA-run missile program. Privately, however, they say it is a crucial tool and has killed several top militant leaders. They also say the drone-fired strikes are very accurate and usually kill militants.
Information from Pakistan's tribal belt is very hard to verify independently. Access to the area is legally restricted, and ongoing conflict there makes it a dangerous territory to venture into.