Two prominent Hong Kong opposition figures were among more than a dozen people arrested in a police operation focused on last year's huge protests, .
Lam Cheuk-ting and Ted Hui were detained after early morning raids on their homes, adding to the mounting prosecutions targeting Beijing's critics.
Both are minority Democratic Party politicians in the city's partially elected legislature and vocal critics of Beijing as well as Hong Kong's government and the police.
"This is out-and-out political persecution," James To, a veteran lawyer and fellow party member, told reporters on Wednesday.
Police said the arrests were related to two anti-government rallies last year: one on 6 July and the other on 21 July, the latter on a day that saw a notorious attack by government loyalists on protesters in the town of Yuen Long.
Lam Cheuk-ting, left, and Ted Hu, right, argue with pro-Beijing politician Junius Ho during a demonstration of an anti-riot vehicle. Source: AAP
The brazen assault by more than 100 mostly white-clad men armed with wooden and metal poles helped fuel months of increasingly violent protests.
Police have charged eight people over the attack, some with links to "triad" organised-crime gangs.
But they are now describing the clash as being between "evenly matched rivals".
"In today's operation, we arrested people who are believed to belong to the other side," senior superintendent Chan Tin-chu told reporters.
Mr Lam, who was beaten bloody in the assault, was among 13 arrested Wednesday on suspicion of rioting, Mr Chan said. The group also included a senior bank official and a social worker, he added.
The Yuen Long attack, which was streamed live, was a defining moment of last year's pro-democracy protests.
Democracy supporters including Mr Lam and Mr Hui have accused police of deliberately arriving late to the scene, allowing the attackers to leave, and botching the subsequent investigation - allegations the force has denied.
Pro-Beijing figures hailed the latest police action.
"Justice may be late but never absent," said politician Junius Ho, who was seen shaking hands with some of the white-clad men in Yuen Long before the attack.
Ho has denied prior knowledge of the assault and said he was simply greeting patriotic locals. On Wednesday he said he has "clean hands that need no washing".
Antony Dapiran, a Hong Kong lawyer who has written books about the city's protests, described the police recasting of the Yuen long attack as "gaslighting of the highest order".
"HK govt and police [are] trying to rewrite the narrative of one of the most documented and live-streamed events of last year," he wrote on Twitter.
