An Afghan worker on the base in Helmand province allegedly ambushed a group of NATO soldiers at about 8 p.m. Friday and fatally shot three of them, the Los Angeles Times reported.
The attack followed another green-on-blue fatality in which an Afghan police commander lured three special-operations U.S. Marines to a meal during the dusk-to-dawn eating hours of the holy month of Ramadan for Muslims. The commander shot and killed the Marines. It was not clear whether the attack happened late Thursday or early Friday.
Both Afghan and Western military officials said the attacks were under investigation, and President Karzai condemned them.
So far this year, 34 Western troops have been killed in Afghanistan in green-on-blue shootings, the newspaper said.
Brig. Gen. Gunter Katz, chief spokesman for NATO, said the recent incidents are not indicative of how Afghan and foreign forces work together overall.
"Those two incidents clearly do not reflect the overall situation here in Afghanistan," Katz said.
Meanwhile, at least 21 Afghan troops have been killed or injured by insurgent attacks over the past 24 hours, Afghan officials said Saturday.
Five Afghan soldiers were killed in Kunar, Paktiya, Logar, Maidan Wardak and Herat provinces of Afghanistan while 16 others were injured, Khaama Press reported.