Real Madrid has launched an investigation into racist insults directed at players during Saturday’s 4-0 home loss to Barcelona in LaLiga, it said on Sunday.

Spanish media reported that 17-year-old Barcelona forward Lamine Yamal, who is of Equatorial Guinean and Moroccan heritage, was targeted with xenophobic and racist abuse at the Bernabeu. Barcelona did not immediately respond to a Reuters request for comment.

“Real Madrid strongly condemns any kind of behavior involving racism, xenophobia or violence in football and sport, and deeply regrets the insults that a few fans uttered last night in one of the corners of the stadium,” Real said in a statement.

The Spanish Football Federation (RFEF) and LaLiga have taken steps to tackle an increase in racist abuse with measures including partial stadium closures.

Four people were arrested and questioned in Spain on Thursday on suspicion of conducting an online hate campaign encouraging fans to racially abuse Real Madrid’s Brazilian forward Vinicius Jr. in the buildup to their match against Atletico Madrid last month.

In June, the Magistrate’s Court of Valencia issued the first conviction for racist insults in a soccer stadium in Spain.