LONDON (AP) — The United Kingdom's antitrust watchdog has blocked Facebook's acquisition of GIF-sharing platform Giphy and ordered the social network to reverse the deal, saying it hurts social media users and advertisers by stifling competition for animated images.

The Competition and Markets Authority said Tuesday that the deal would let Facebook “increase its already significant market power” by denying or limiting other platforms' access to Giphy GIFs and driving traffic to Facebook-owned sites.

It's reportedly the first time the watchdog has sought to unwind a tech deal.

“By requiring Facebook to sell Giphy, we are protecting millions of social media users and promoting competition and innovation in digital advertising," said Stuart McIntosh, chair of the group that carried out the investigation.