The RAF has launched an investigation over photos apparently showing at least one serviceman posing beside the body of a dead Taliban insurgent in Afghanistan.
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The US president, who has not visited the UK since being elected, is reported to be planning a summer trip to Britain.
Mack entered her plea in federal court in Brooklyn. The judge refused a request by her lawyers to release her without bail.
Officers investigating a reported break-in on Friday found 22-year-old Roger Alvarado asleep in the pop star's home in Tribeca.