Listen to Wayne Mills Band on iHeartRadio

Blake Shelton is among those expressing his grief over the death of fellow country singer Wayne Mills. 

Nashville's "Tennessean" says Mills was shot early Saturday morning at the Nashville bar Pit and Barrel.  Bar owner Chris Ferrell admits to the shooting.  He's told police Mills was smoking in the bar which led to an argument that escalated, and the shooting was in self-defense.  Nashville police spokeswoman Kris Mumford says no arrests have been made yet, and the matter is still under investigation.  Mills was 44. 

Shelton tweeted Sunday that he's "extremely sad" to hear about Mills' death, calling him an "old friend." 

Shelton, Jamey Johnson, and former "American Idol" winner Taylor Hicks are among those who worked with Mills earlier in their careers, opening shows for the Wayne Mills Band.