Cricket chiefs are investigating claims India players received racist abuse from crowd members on day three of the third Test against Australia, while six people were ejected on day four.
In a further incident on Sunday, play was halted for 10 minutes after Siraj told the umpires of more alleged abuse.
Cricket Australia and New South Wales police are investigating this incident.
Siraj walked in from fine leg shortly before the tea break to speak to team-mates and umpires Paul Reiffel and Paul Wilson before pointing to a section of the Sydney Cricket Ground crowd.
Police subsequently removed six spectators from the stadium, although it is not yet clear what had been said to Siraj.
CA's head of integrity and security Sean Carroll said the allegations would be investigated "to their fullest extent".
"The abuse of cricketers by crowd members is not acceptable," he said. "We thank the Indian team for their vigilance in reporting Sunday's incident, which we are now in the process of investigating.
"While we await the outcome of the investigation by NSW Police, CA has launched its own inquiry into the matter.
"It is most regrettable that an otherwise excellent Test match contested in tremendous spirit by two friendly rivals has been tarnished by the actions of a small number of spectators over the past two days.
"As hosts, we once again apologise to the Indian team."
Referring to the alleged racist abuse on Saturday in an earlier statement, CA said it "reaffirmed its zero-tolerance policy towards discriminatory behaviour in all forms" following the alleged racist abuse on Saturday.
Carroll said: "If you engage in racist abuse, you are not welcome in Australian cricket.
"CA is awaiting the outcome of the International Cricket Council's investigation into the matter reported at the SCG on Saturday.
"Once those responsible are identified, CA will take the strongest measures possible under our Anti-Harassment code, including lengthy bans, further sanctions and referral to New South Wales police.
"As series hosts, we unreservedly apologise to our friends in the Indian cricket team and assure them we will prosecute the matter to its fullest extent."
Indian team management spoke to CA chief executive Nick Hockley and Carroll after the close of play on day three.
A group of India players, including captain Ajinkya Rahane, also spoke to the umpires.
Members of the India team staff talked to Bumrah while he was fielding on the boundary towards the end of the final session.
Bumrah and Siraj were also seen talking to officials from Cricket Australia, the International Cricket Council and stadium security.
The crowd has been limited to 10,000 fans per day because of social distancing measures at the SCG, which has a maximum capacity of 48,000.
India closed day four on 98-2, requiring 309 more runs to win after Australia declared on 312-6, setting the tourists an unlikely 407 for victory.
The four-match series is level at 1-1.