A senior US military official has told NBC News that the Nato soldier killed by an Afghan Local Police officer in the east of the country was an American.
Earlier two British troops were shot dead by an Afghan soldier.
16 Nato servicemen have been killed by Afghan Security forces so far this year.
More top news
In the unexpected announcement on Monday, Mr Key said it was the "right time" to leave politics.
As the Government's Brexit appeal comes to the Supreme Court, here's a look at what you need to know.
According to local reports, the man was found by friends in their accommodation in Val Thorens resort in the Alps on Sunday morning.