* Fire starts in forest * Mountain bike course to be assessed on Tuesday (Adds Rio 2016 statement) RIO DE JANEIRO, Aug 15 (Reuters) - A fire was threatening the course that will stage the Olympic mountain bike competition on Monday after a controlled rubbish burn spread out of control in high winds. Photographs posted on the Twitter page of a Canadian Cyclist website showed flames licking the hills surrounding the venue at Deodoro, 43km (27 miles) from the main Olympic Park. "We are aware that there was a fire this afternoon in the vicinity of the Rio 2016 Mountain Bike course," it said. More...