Afghan officials say an Afghan police commander has shot and killed three U.S. service members after inviting them to dinner at his checkpost in southern Afghanistan.

Pentagon officials confirmed that a man wearing an Afghan army uniform killed the special operations Marines late Thursday in the Sangin district of Helmand province. Afghan authorities say the Afghan commander fled the scene after opening fire.

A Taliban spokesman said the attacker joined the insurgency after the attack.

It was the third time this week that international forces have been fired on by their apparent Afghan counterparts.

NATO troops killed an Afghan solider Thursday who tried to gun down coalition service members at a military base in eastern Afghanistan.

On Tuesday, NATO says two gunmen wearing Afghan National Army uniforms killed a coalition soldier in the east.

More than 33 coalition service members have been killed this year in so-called “green-on-blue” attacks. “Green on blue” is a reference to the color of Afghan and NATO uniforms.

NATO spokesman Brigadier General Gunter Katz told reporters in Kabul that the “isolated” incidents “don't reflect the overall situation” in Afghanistan and will have “no effect” on the security transition.

Elsewhere in Helmand, the British Ministry of Defense said a British soldier was killed Friday after coming under insurgent fire while on patrol in the Nad Ali district.

This week has been particularly deadly for international forces, with three coalition soldiers killed in a suicide attack on Wednesday in Kunar province. An Afghan civilian and a USAID Foreign Service officer were also killed in that blast.

Also in Helmand on Friday, Afghan officials say a roadside bomb killed six Afghan civilians, including women and children, in the Musa Qala district.