NATO says three coalition troops were killed Monday by Afghan security forces in two separate incidents.

NATO officials said that, in the first incident, two British soldiers were shot dead at a NATO base in Lashkar Gah in southern Helmand province.

Coalition troops returned fire, killing the attacker, who was wearing an Afghan army uniform.

Hours later, another coalition service member died following a shooting incident in eastern Afghanistan. NATO says the soldier was shot by an alleged member of the Afghan local police while approaching a police checkpoint.

Afghan and coalition forces are investigating the circumstances surrounding the incidents.

Following the incident in Helmand, the province's governor strongly condemned the attack, offering sympathy to the victims' families and praising the sacrifices of NATO forces in Afghanistan.

U.S. officials say there have been at least 42 attacks by Afghans on their NATO colleagues since 2007.

The attacks come two weeks after a U.S. soldier allegedly went on a shooting spree in Afghanistan, further straining relations between Afghans and NATO forces.

Army Staff Sergeant Robert Bales, an 11-year military veteran, faces charges that include 17 counts of murder and six counts of attempted murder. He is alleged to have walked out of his southern Afghanistan military base under the cover of darkness March 11, gunning down nine children and eight adults in nearby villages.