The home secretary has demanded a "full explanation" from Twitter and Instagram on why anti-Semitic posts by rapper Wiley were not removed more quickly.
Police are investigating a series of posts on the grime artist's social media accounts. He has been temporarily banned from both Twitter and Instagram.
Priti Patel said the posts were anti-Semitic and "abhorrent".
"Social media companies must act much faster to remove such appalling hatred from their platforms," she said.
Wiley, 41, known as the "godfather of grime", shared conspiracy theories and insulted Jewish people on his Instagram and Twitter accounts, which together have more than 940,000 followers.
The antisemitic posts from Wiley are abhorrent.— Priti Patel (@pritipatel) July 26, 2020
They should not have been able to remain on Twitter and Instagram for so long and I have asked them for a full explanation.
Social media companies must act much faster to remove such appalling hatred from their platforms.
Twitter removed some of Wiley's tweets with a note saying they violated its rules - but other tweets were still visible 12 hours after being posted. It later said Wiley's account had been locked for seven days.
Facebook - which owns Instagram - said on Sunday that the platform had also blocked the rapper from his account for seven days, and that there was "no place for hate speech on Instagram".
But Mayor of London Sadiq Khan said the steps taken by Twitter and Instagram were not enough.
In a letter to bosses of the two social media firms, he said that when the material was published on their platforms, "the response - its removal and the banning of those responsible - should be immediate.
"It takes minutes for content shared on your platform to reach an audience of millions. When someone influential shares hate speech, in that time it may have an impact on the views of many who look up to them."
Mr Khan said it was "particularly disheartening" when social media had played a "positive role in amplifying the vital voices" of the Black Lives Matter movement recently.
Wiley's series of posts began on Friday night and his manager John Woolf's initial response was that, having known the artist for 12 years, "he does not truly feel this way".
But on Saturday, Mr Woolf said he had "cut all ties" with the London-born rapper and that there was "no place in society for anti-Semitism".
Wiley first entered the UK singles charts with Wearing My Rolex in 2008. His subsequent hits include Heatwave in 2012 and Boasty in 2019, a collaboration with rappers Stefflon Don and Sean Paul and actor Idris Elba.