The suspected US drone fired two missiles at a house owned by a local tribesman in the Pakistani region of North Waziristan, the officials said. At least three of the dead were said to be German - of Arab or Turkish origin.

In recent weeks, security sources have spoken of a Pakistan-linked al-Qaeda plot to attack European cities.

US media outlets reported that the Central Intelligence Agency (CIA) had ramped up missile strikes from its unmanned drones, targeting militants who are believed to have inspired the alleged plot.

In Pakistan, the US has carried out 26 drone strikes in the past month - the highest monthly total for the past six years. The suspected plot has led several countries to issue travel warnings to their citizens, saying they should be vigilant while travelling in Europe.

Although there has been no official comment on the latest drone strike, there have been lingering concerns over German nationals in the tribal areas.

German media has been reporting since 2009 about the disappearance of several Islamist militants from their homes in Hamburg, thought to have headed to Pakistan's tribal areas.

The arrest of one of those militants earlier in Afghanistan earlier this year is said to have yielded useful intelligence to German investigators.