The Premier League said it was treating “tragedy chanting” as a “matter of urgency” after extremely obnoxious behavior by Leeds and Manchester fans inside Elland Road prompted a joint statement of condemnation from both clubs.

Leeds fans sang about the 1958 Munich air disaster, in which eight Manchester United players were among the 23 killed. Traveling fans responded with a similarly moronic song about the events of 2000 in Istanbul, in which two Leeds fans died.

The chanting was described as “completely unacceptable” in the clubs’ joint statement, and they promised to work with their respective fan groups and the Premier League to eliminate it.