At least six protesters were killed by security forces in Burma (also known as Myanmar), witnesses and media reported, as activists marked the anniversary on Saturday of a student whose killing in 1988 sparked an uprising against the military government. Three people were killed and several injured when police opened fire on a sit-in protest in Mandalay, Burma’s second-biggest city, two witnesses told Reuters. Another person was killed in the central town of Pyay and two died in police firing in the commercial capital Yangon overnight, domestic media reported. “The security forces initially stopped the ambulance from reaching the injured people and only allowed it later,” a 23-year-old protester in Pyay told Reuters, asking not to be named for fear of retribution. “By the time they allowed it, one of the injured became critical and he later died.” The deaths came as the leaders of the United States, India, Australia, …