Nice - A Northern Ireland fan became the first fatality at Euro 2016 after plunging to his death from a guard rail overlooking the sea in the French city of Nice, a police source said.
The young fan, who was in his twenties, fell between seven and eight metres into the Mediterranean at around 02:00, the source told AFP.
"On behalf of the Irish Football Association, I would like to express my deep sadness at the tragic death of a Northern Ireland supporter," said Patrick Nelson, CEO of the Irish FA, in a statement.
"The thoughts of everyone at the Association are with his family and friends at this time."
An investigation was underway to determine the cause of his death, which was believed to be accidental and have no link to the clashes between fans that marred the opening of the tournament in nearby Marseille at the weekend.
Northern Ireland played their first game of the tournament on Sunday in Nice, losing 1-0 to Poland.
By contrast with the violence during Saturday's England-Russia game in Marseille, the game in Nice passed off without incident.
But a day before the match in Nice seven people were injured in the city after scuffles broke out between French locals and Northern Ireland supporters following the England-Russia game.