An Afghan civilian employed on a NATO base in southern Afghanistan shot dead three international coalition soldiers last night, the same day three others were killed by an Afghan policeman, ISAF said on Saturday. "The shooter was not in uniform and our current reporting indicates he was a civilian employee authorized to be on the base, but there is no indication he was an Afghan service member," an ISAF spokesman said. The spokesman said he had no information on how the civilian got hold of a weapon on the shared Afghan-Nato base in southern Afghanistan, and provided no further details. Also on Friday, an Afghan police officer opened fire on four American soldiers he had invited for a meal, killing three of them, Afghan officials said, in the third so-called green-on-blue assault in just four days. The US military in Afghanistan confirmed that three US soldiers had been killed by "an individual in an Afghan uniform" in Sangin district of southern Helmand province, but gave no further details.