Gunmen wearing Afghan police unfoirms killed 3 US soldiers, NATO said, according to the BBC.
An anonymous senior Afghan official told Reuters:
"During dinner, the police commander and his colleagues shot them and then fled. The commander was Afghan National Police in charge of local police in Sangin," a senior Afghan official told Reuters on condition of anonymity.
"It looks like he had drawn up a plan to kill them previously," the official said.
A NATO spokeswoman said they could not confirm if the incident was part of a larger insurgent infiltration, or if it was an isolated rogue shooting.
"All we know is that they were killed by an Afghan in a uniform of some sort," the spokeswoman said.
These kind of attacks are called green-on-blue shootings.
According to Reuters, there were 24 attacks last year that fit this description.
Brig Gen Sherin Shah of the Afghan National Army (ANA) said in May, according to BBC:
"We do our best, our intelligence departments try to prevent [the] entering of enemies into the Afghan National Army but [we] cannot promise that it will not happen again... I can't say anything about it, it is out of my control."