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 KABUL—Two U.S. soldiers were shot dead by trusted Afghan colleagues on Thursday, the third such incident since riots erupted a week ago over the burning of Qurans at an American airfield north of Kabul. 
 
 The predawn attack at a base in southern Kandahar province brought to six the number of U.S. troops killed by Afghan security personnel in eight days. No U.S. or coalition personnel were killed in combat or by roadside bombs in the same period. 
 
 Thursday's shooting amplified the new dangers facing American-led forces as they try to wind down combat operations in Afghanistan and cede security control ... 

 A U.S. official says two more American troops have been killed in Afghanistan, the latest in a series of attacks following protests over the burning of the Quran. 
 
 The official said details of the killings Thursday in southern Afghanistan are still unclear, but officials believe there were three attackers, two of whom were subsequently killed. He said the third may be in custody. 
 
 The official spoke on condition of anonymity because he was not authorized to speak on the record.
– Increasingly frightening news out of Afghanistan: Two more US troops died at the hands of their Afghan colleagues today, bringing the death toll of such green-on-blue attacks in the last eight days to six. The service members were killed before dawn at a southern Kandahar base, marking the third such instance since the protests over Koran-burning began last week. A third US service member was wounded, reports the Wall Street Journal. Reports on the gunmen are conflicting: Coalition reports cited two men, only one dressed as a soldier; the governor of the district where the shooting occurred says a literacy teacher assisting the Afghan National Army took a gun from an Afghan soldier and began firing. And the AP places the number of attackers at three. While those numbers are hazy, these aren't: The Journal reports that not a single US or NATO soldier was killed by bombs or in combat since the protests erupted; in 2012, one out of every five coalition-troop deaths can be attributed to an Afghan colleague.