"One of the injured died in intensive care as a result of the attack," Ekho Moskvy radio station quoted one of the environmental activists, Olga Kozlova, as saying.

Another resident of the camp, Marina Popova, said the attackers shouted slogans against anti-fascists.

"From that we can conclude they were Nazis or skinheads", she told the Vesti-24 television channel, blood seeping through a bandage wrapped around her head.

Environmentalists have not previously been the target of violent attacks in Russia, where skinhead gangs have assaulted and killed people from ethnic and religious minority groups in the past.

Itar-Tass news agency said the man killed on Saturday was a 20-year-old from the far eastern port city of Nakhodka.

Thirteen attackers had been identified and four had already been arrested, said Interior Ministry spokesman Valery Gribakin.