DUBAI, United Arab Emirates — Two U.S. Navy pilots were shot down Sunday over the Red Sea in an apparent "friendly fire" incident, the U.S military said, marking the most serious incident to threaten troops in over a year of America targeting Yemen's Houthi rebels.

"The guided missile cruiser USS Gettysburg, which is part of the USS Harry S. Truman Carrier Strike Group, mistakenly fired on and hit the F/A-18," Central Command said in a statement.