Warning of "imminent" attack, Britain raises threat level

MANCHESTER, England — As officials hunted for accomplices of a suicide bomber and Britain's prime minister warned another attack could be "imminent," thousands of people poured into the streets of Manchester in a defiant vigil Tuesday for victims of a blast at a pop concert — the latest apparent target of Islamic extremists seeking to rattle life in the West.The attack left at least 22 dead, including an 8-year-old girl, shattering the revelry at a show by American singer Ariana Gran