Lazio have blamed "isolated elements" within their fan base after racist chants were directed at AC Milan's Tiemoue Bakayoko around the Coppa Italia semi-final.
According to reports in Italian media, insults by Lazio fans were made about Bakayoko, on loan from Chelsea, outside San Siro ahead of the game and during the warm-up on Wednesday night.
Fellow Milan midfielder Franck Kessie is also understood to have been subjected to racism, while inflatable bananas were visible in the away section.
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Earlier in the day, a group of Lazio fans unfurled a banner reading "Honour to Benito Mussolini" in the city centre at the scene of where the fascist dictator was killed at the end of World War II.
"Lazio takes clear distances from behaviour and events that do not reflect in any way the sporting values sustained and promoted by the club for 119 years," the Serie A club said in a statement.
"And it rejects and disputes the simplistic tendency of some media to consider the entire Lazio support jointly responsible for acts carried out by a few and isolated elements, for reasons foreign to any form of sporting passion."
There were two announcements over the speaker system at San Siro warning the fans to stop or the match would be suspended.
The incidents follow shortly after racist insults were aimed at Juventus striker Moise Kean during his team's Serie A victory at Cagliari earlier this month.
Inter Milan were ordered to play two home league matches behind closed doors after Napoli defender Kalidou Koulibaly was subjected to racist insults during a match at San Siro in December.
Lazio won Wednesday's Coppa Italia semi-final second leg 1-0 to progress to the final, where they will meet either Atalanta or Fiorentina.