Meanwhile, Swansea reported that defender Rhys Williams was subjected to racist abuse from a home spectator during the second half of their match against Luton at Kenilworth Road.
Peterborough said in a statement: “Peterborough United Football Club can confirm that two Birmingham City supporters have been arrested following the allegation of racism aimed towards defender Nathan Thompson during the second half of Saturday’s Sky Bet Championship fixture at the Weston Homes Stadium.
“Thompson reported the incident straight away to the match official who spoke with the fourth official before the two individuals were identified and detained.
“The football club condemns any form of discrimination and will work with the authorities.”
Birmingham said in a statement that the club have a “zero-tolerance policy towards any form of discrimination” and that they “will continue to assist the police in their investigations” and would “firmly support the action taken against anyone found guilty of such abhorrent behaviour.”
Swansea confirmed they had filed an official report alleging the abuse against Williams, and added that Bedfordshire Police and Luton were working to identify the individuals involved.
The club continued: “Swansea City condemns racism and abuse of all kinds because it has no place within football or any walk of life.
“Rhys has the full backing of everyone at the football club and we are in dialogue with his parent club Liverpool with regards to ensuring the player has all the support he needs.”
The Anfield club later tweeted in support of their player: “We’re with you, @rhyswilliams01 . #RedTogether.”
Also on Saturday, Kelty Hearts striker Nathan Austin was subjected to racist abuse during his team’s cinch League Two victory over Albion Rovers.
A Rovers fan group confirmed the abuse had taken place and said the perpetrator had “owned up to it and has been removed from our group.”