Cambodian security forces have opened fire on protesting garment workers on the outskirts of the capital Phnom Penh, killing at least three people.Military police fired warning shots in the air and then fired at protesters on Friday, leaving at least three people dead."Three people died and two were injured," Phnom Penh deputy police commissioner Chuon Narin said.The incident happened after thousands of workers blocked the road in front of factories and later faced off with security personnel in the Veng Sreng area of Phnom Penh. The workers are among 350,000 on strike, demanding higher pay.