Afghan infiltrator kills US soldiers
Three American soldiers are dead after being gunned down by an Afghan soldier in Nangarhar province.
The Taliban has claimed responsibility, saying the shooter was an infiltrator.
A fourth US soldier has been injured.
The so-called 'green-on-blue' insider attacks on American troops were a major problem several years ago.
Nangarhar province was also the site of the United States' 'mother of all bombs' attack in April.