The Pentagon chief said on Tuesday the U.S. military "deeply regrets" the loss of life in an American strike on an Afghan hospital in Kunduz and is acknowledging its mistake and working to understand what went wrong.

"The U.S. military takes the greatest care in our operations to prevent the loss of innocent life, and when we make mistakes, we own up to them. That's exactly what we're doing right now," Defense Secretary Ash Carter said in a statement.