WASHINGTON (Reuters) - Militants are showing renewed interest in using a surgically implanted bomb to blow up a commercial flight, though there is no indication an attack is imminent, a U.S. security official said on Wednesday, citing new intelligence. U.S. authorities have warned their counterparts abroad as well as air carriers about the new information and were taking steps to boost security. "The Department of Homeland Security has identified a potential threat from terrorists who may be considering surgically implanting explosives or explosive components in humans to conduct terrorist attacks," the advisory to foreign counterparts said, according to the U.S....