Hong Kong police have admitted to having some of their officers pose as protesters during Sunday’s demonstrations after video and images went viral showing the plainclothes officers making arrests.

The officers, dressed in black and wearing helmets, were seen helping to pin some of the protesters to the ground following a clash at Causeway Bay. They have received criticism for reportedly failing to show any warrant cards while helping to make the arrests and for refusing to answer journalists afterward when they were questioned about being police officers.

A group of plainclothes officers, disguised as protesters, launched a surprise operation to arrest protesters outside SOGO department store in Causeway Bay. At least a dozen were arrested. The officers refused to answer reporters' questions on their identity.#HongKong #antiELAB pic.twitter.com/P3WzYCJdu7 — Hong Kong Free Press (@HongKongFP) August 11, 2019

Check out this Twitter thread from Bloomberg’s Alice Truong for a quick breakdown.

Many other seeming plainclothes police officers pic.twitter.com/3uflyT2OD8 — Alice Truong (@alicetruong) August 11, 2019

One giveaway of plainclothes police officers seems to be the baton, as this reporter points out. They seem to have a more discrete telescoping baton pic.twitter.com/aYiMxWSUOB — Alice Truong (@alicetruong) August 11, 2019

and their earphones. pic.twitter.com/MrkuH9BAEv — Hong Kong Police Record (@hkpolicerecord) August 11, 2019

At a press conference on Monday, Hong Kong police acknowledged that several officers had been disguised as protesters, characterizing the move as part of an operation which targeted “extremely violent rioters” who were using weapons like petrol bombs against police.

As for rather the officers had broken police regulations, a spokesperson said that the officers would try their best to show their identity while making the arrests and would not incite protesters into any radical or violent acts.