PESHAWAR, Pakistan — Three US missile strikes hours apart killed 18 people in a militant stronghold near the Afghan border in northwest Pakistan on Saturday, two Pakistani intelligence officials said.At least nine people were killed in the first strike when missiles destroyed a moving vehicle in the North Waziristan tribal region, the officials said.Two hours later drones fired more missiles that struck people who had gathered to retrieve the bodies, killing five. A third strike Saturday evening once again targeted a moving vehicle in the Mohammed Khel area of North Waziristan, killing four people, they said.