Four U.S. service members were killed in the past 24 hours in Afghanistan, NATO forces said Monday, AP News Agency reported. Three of the Americans died in southern Afghanistan on Sunday, the statement said. Two of them were killed by a bomb attack and the third in a separate firefight. The military said the fourth U.S. service member died in the east Monday in a bomb explosion.The deaths bring the number of Americans killed in Afghanistan in November to 15. October was the deadliest month for U.S. troops in the eight-year war, with 58 dead. Meanwhile, Afghan officials said three Afghan army soldiers were killed by a roadside bomb in southern Helmand province. The Interior Ministry said the bombing occurred on Sunday in Musa Qala district. It did not give further details and it was not clear if there was any connection between the Afghan deaths and the American deaths.