GELSENKIRCHEN, Germany — Schalke has apologized for its fans' racist abuse of Borussia Dortmund youth player Youssoufa Moukoko during a match between the rival clubs' under-19 sides on Sunday.

"Derby emotions aside, we completely condemn and oppose such insults," Schalke said on Twitter.

In a tweet with the hashtag "NoToRacism," the club said its supporter relations department "will take the necessary measures."

Some Schalke fans can be heard abusing the 15-year-old striker on video after he scored his third goal from distance against their side in the 63rd minute.

"It has to be condemned in the strongest possible terms," Schalke's sporting director Jochen Schneider said before Schalke's Bundesliga game against Union Berlin on Sunday. "It's becoming impossible to put into words what some people allow themselves (to do)."

Only around 300 supporters with personalized tickets were allowed at the game due to coronavirus restrictions, so Schneider said he hoped it would be possible to find the perpetrators. He said he apologized on behalf of Schalke to Moukoko and Dortmund chief executive Hans-Joachim Watzke.

Schalke coach Manuel Baum said values were a top priority for him, "so how the club has positioned itself was exactly the right reaction."

Moukoko, who is Black, will be eligible for Dortmund's senior team when he turns 16 on Nov. 20. He scored a hat trick in the under-19s' 3-2 Ruhr derby win. It was his third hat trick in three competitive games after a 3-0 cup win against SV Wehen Wiesbaden and 5-0 league win at Preußen Münster.

Dortmund reacted to the abuse of the player with a tweet containing the hashtag "NoToRacism."