The U.S. military’s top officer acknowledged this week that rampant “insider” attacks by Afghan forces on their American and NATO allies pose a “very serious threat” to the U.S. war effort, which could play havoc with the White House’s plan to leave the country in the next two years.

In an interview with the American Forces Press Service (AFPS), Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey said the growing problem of Afghan military and police forces turning their guns on American soldiers cannot be tolerated any longer.