A US drone attack killed at least three militants in North Waziristan on Monday, the second such strike in 24 hours, security officials said. Officials said the US aircraft fired at least one missile into a vehicle as it left a village in North Waziristan. "The US drone fired one missile, which hit a vehicle. According to our reports, three militants were killed," a security official told AFP on condition of anonymity because he was not authorised to speak to the media. Local officials put the death toll at four, saying the drone targeted a vehicle carrying militants just as they were leaving Tabi Ghundi Kala village. "It was a drone attack. Two missiles were fired into the vehicle. Four militants were killed," said a local security official. The identities of the dead were not immediately clear, nor was it known if they were high-value targets. US drone attacks in North Waziristan have increased since Mehsud appeared in a video alongside a Jordanian Al-Qaeda double agent claiming responsibility for a suicide attack on CIA agents across the border in Afghanistan. The December 30 attack at a US base in Khost province killed seven CIA employees in the deadliest attack on the US spy agency in 26 years. It came one day after a similar attack killed seven militants at an Islamist training compound in North Waziristan. The Pakistan government publicly condemns the strikes saying they violate the nation's sovereignty, but analysts say Islamabad gives tacit approval to its US ally for the raids. More than 780 people have been killed in the US strikes in Pakistan since August 2008, and American officials say they are a vital tool in the battle against militants and have killed a number of high-profile targets. Mehsud's predecessor, Baitullah Mehsud, who founded Tehreek-e-Taliban Pakistan (TTP), blamed for the deaths of thousands of people in Pakistan, was killed in a US drone strike in August last year.