The attacks have drawn stiff protests from Islamabad, an uneasy ally in Washington's seven-year war on terror, particularly since a highly unusual Sept. 3 raid by U.S. ground troops in the South Waziristan region.
The two intelligence officials said the missiles struck the home of a local Taliban commander before midnight Tuesday near Mir Ali, a town in the North Waziristan region.
The officials, citing reports from their field agents, said six people were killed. Both officials asked for anonymity because they were not authorized to speak to media. They said a U.S. drone aircraft - not Pakistani forces - fired the missiles. They did not identify any of the victims.
Pakistani leaders insist only their forces are allowed to carry out operations inside Pakistan, and its troops recently fired warning shots at U.S. helicopters flying over the ill-marked frontier.
American officials have expressed frustration at Pakistan's failure to kill or capture militant leaders whom they accuse of sending fighters and arms into Afghanistan, where foreign troop casualties are escalating.
In Spain, a radio station reported that a document marked confidential and bearing the official seal of Spain's Defense Ministry charges that Pakistan's spy service was helping arm Taliban insurgents in 2005 for assassination plots against the Afghan government.
The report, which was obtained by Cadena Ser radio and posted on the station's Web site on Wednesday, also says Pakistan's Inter-Services Intelligence spy agency, or ISI, helped the Taliban procure explosives to use in attacks against vehicles.
It alleges that Pakistan may have provided training and intelligence to the Taliban in camps set up on Pakistani soil.
There have long been suspicions that members of Pakistan's shadowy spy agency have aided the Taliban, a charge that Pakistan has vehemently denied. In the 1990s, however, the ISI's agents helped build up the Taliban.
Pakistan's chief army spokesman Maj. Gen. Athar Abbas said the report was "baseless, unfounded and part of a malicious, well-orchestrated propaganda campaign to malign the ISI."
Spain's Defense Ministry and the Spanish prime minister's office said it had no comment. Cadena Ser did not say how it obtained the report.
Meanwhile, a physician for the Taliban and a spokesman for the group denied reports that the movement's top leader in Pakistan, Baitullah Mehsud, had fallen ill and died.
"I spoke to him today at 9 a.m. on the telephone and he told me that he is surprised over rumors about his death," physician Eisa Khan told The Associated Press. Khan said Mehsud had an unspecified kidney problem but gave no more details.
Mehsud's spokesman, Maulvi Umar, was cited on Geo television station as saying he was healthy.
Officials have accused Mehsud of being behind a wave of suicide attacks washing over Pakistan since the middle of last year, including the slaying of opposition leaders Benazir Bhutto in December.
Associated Press writers Riaz Khan in Peshawar and Ishtiaq Mehsud in Dera Ismail Khan contributed to this report.