Police are investigating allegations of homophobic chanting by West Ham fans at Chelsea on Saturday.
Metropolitan Police officers were contacted on social media to report chanting by away fans directed at Chelsea fans at Stamford Bridge.
The force said in a statement on Monday that “enquiries are ongoing” but no arrests have been made.
Anti-discrimination charity Kick It Out has also called on the Football Association to investigate.
Chelsea Supporters’ Trust said it noted “with dismay the continuous homophobic chanting by visiting West Ham fans”.
West Ham LGBT+ Supporters’ Group, Pride of Irons, says Kick It Out have made clear these chants were homophobic.
It added on Twitter: “When you use homophobic chants you aren’t abusing most Chelsea fans who will be straight, but all gay fans whether they support Chelsea or West Ham.
“We’re better than that and can come up with much smarter chants that don’t abuse our own fans.
“We shouldn’t be the club appearing in the news for homophobia… there are other clubs who have ingrained problems.
“Let’s not join their ranks. Be better. Be West Ham. Support the whole West Ham Family, no matter race, gender, sexuality or anything else.”
It is understood the FA is aware of the allegations and discussions with relevant authorities are ongoing.
A Chelsea spokesman said: “Just as we criticise our own supporters when they have been guilty of discriminatory behaviour, we expect other clubs to stand up, speak out and do the same.”
In a statement, West Ham said: “West Ham United in no way condones any behaviour that falls short of the highest standards which the club sets when it comes to equality.
“At London Stadium against Arsenal on Monday night we will be celebrating and demonstrating the great work the club does to create a welcoming and inclusive environment for ALL supporters, including our LGBT+ fanbase, as part of our ongoing and unwavering support for the Rainbow Laces campaign.”
Aaron Cresswell scored the winner as West Ham won 1-0 in the Premier League on Saturday.