Seven Hong Kong police officers were charged Thursday with assaulting a pro-democracy protester in a beating captured on video -- but the victim was also charged in the heavily-criticised case.

It comes one year to the day since the attack on Civic Party activist Ken Tsang, footage of which was beamed around the world at the height of mass protests for free leadership elections in Hong Kong.

"Seven police officers have been jointly charged with one count of causing grievous bodily harm with intent," a police spokeswoman said Thursday.

Those charged were later named for the first time by the justice department and include senior officers.

One chief inspector is from the Organised Crime and Triad Bureau, the unit tasked with fighting the city's notorious gangs, according to local media.

Tsang, 40, said he was also charged with attacking 11 police officers and slammed the allegations as "unreasonable and ridiculous".

He attended a police station in central Hong Kong Thursday and said he was charged with assault and four counts of obstruction.

Tsang said he had been given no detail of the incidents the charges referred to, except that they all took place on October 15, the night he was beaten.

He was released on bail.

The justice department later said the assault charge was brought because Tsang "splashed liquid from a plastic container" onto police and had then obstructed officers by resisting arrest.

The statement added the officers Tsang allegedly splashed were not those accused of subsequently attacking him.

One of the seven officers charged is also facing an allegation of common assault on Tsang which the justice department said happened in an interview room after his arrest.

- Video footage -

Video footage aired by local television network TVB showed a group of men hauling a handcuffed Tsang to a dark corner in a public park in the early hours of October 15 last year.

One stands over him and punches him, as three others are seen repeatedly kicking him, in a case that rocked the reputation of the city's respected police force.

Seven officers were arrested in November and suspended from duty over the attack but the case then stalled.

The authorities withheld the identities of the seven involved, believed to be plainclothes police, and the delay in bringing the case to court has been criticised by Tsang and his supporters.

Tsang said the charges brought against him Thursday were a ploy to "dilute" the case against the police.

His lawyer Michael Vidler said the fact that Tsang would appear in court Monday, at the same time as his suspected attackers, was "indicative of the fact they want to blacken his name".

"When you go to court and there is coverage of these seven officers, you will also be reporting these multiple charges against my client," he told reporters outside the police station.

Tsang was granted permission in July for a judicial review challenging the authorities' previous decision not to identify his assailants.

He and his legal team argued that if the names were revealed they could pursue the case privately, in the event the public case fails.

A number of pro-democracy protesters have been arrested since rally camps were cleared in December.

One woman was sentenced to three-and-a-half months in jail in July after a court found her guilty of using her breast to bump into a police officer during a chaotic protest.