St. Petersburg, May 26 (IANS/RIA Novosti): In a rare display of public humility, the head of police in Russia's St. Petersburg city publicly apologised to motorist rights activists after they were allegedly beaten up by policemen.

But Sergei Umnov's apology, published on the city police's website, never specified what caused the conflict between traffic police and activists of the Blue Buckets group.

The victims said they chided two traffic police officers in Kolpino outside St. Petersburg for parking on the sidewalk.

But then they were suddenly jumped by five men in plainclothes, including at least one more traffic police officer, Blue Buckets said in their Livejournal community, ru-vederko.

The "attackers" beat up the activists in plain view of the officers on duty, who smiled and refused to interfere, the report said.

One of the victims was hospitalised with skull fracture and possible kidney trauma.

Three officers involved in the incident have been sacked, along with three of their bosses.

However, only one of the alleged participants of the fight faced charges so far, with regional prosecutors saying they were unable to identify the other attackers.

Motorist groups are among Russia's most active civil society movements, campaigning against alleged rampant abuse of traffic rules by state servants, many of whom are entitled to various road privileges.