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Facebook, Twitter, Google and Microsoft are not acting quickly enough to tackle hate speech, according to the European Commission, which has told the companies to get their act together.

If the Silicon Valley companies do not speed up their response to tackling illegal hate speech on their platforms, they will be be held accountable under European law, the Commission said Sunday.

Back in May, the companies all voluntarily signed up to a code of conduct, in which they promised to remove hate speech within 24 hours of it being posted and to promote counter-narratives. The code arose from concerns about a proliferation of hate speech on the platforms following a spate of terror attacks in Europe and amid the refugee crisis.

Signing the code was an alternative to the EU drawing up laws on the matter. But now the EU Commissioner for Justice, Vera Jourova, has said that the Commission may be forced to enact laws after all, as only 40 percent of posts are being removed within the time frame.

"If Facebook, YouTube, Twitter and Microsoft want to convince me and the ministers that the non-legislative approach can work, they will have to act quickly and make a strong effort in the coming months," she told the Financial Times.

The Commission also noted that the volume of hate-speech posts removed within 24 hours differs dramatically across Europe. In France and Germany, over 50 percent of posts are taken down, but in Austria and Italy, the rate drops to 11 percent and 4 percent, respectively.

"After 48 hours the figure is more than 80 percent. This shows that the target can realistically be achieved, but this will need much stronger efforts by the IT companies," Jourova said to Reuters.

Facebook, Twitter, Google and Microsoft did not immediately respond to requests for comment.