A Russian court has ordered 20 Greenpeace activists from around the world to be held in custody for two months, while investigations continue into their protest at a Russian Arctic offshore oil platform.

A freelance press photographer and a cameraman were also ordered to be held for two months, while eight more activists will have their cases reviewed in three days.

The group were arrested by armed Russian security services at sea when some tried to scale the giant oil platform.

They appeared in court in the port of Murmansk handcuffed and in cages.

Among those held are crew from the Greenpeace vessel Arctic Sunrise from which the protest was launched.

The environmental group was protesting against the environmental risks of oil and gas exploration in the Arctic.

Russian state prosecution authorities have launched a criminal case on suspicion of piracy, punishable by up to 15 years in jail.

The activists have not yet been charged.

Greenpeace has ridiculed the piracy allegations, saying all its protests are peaceful.

The 30 held included six Britons and four Russians as well as nationals of Argentina, Canada, the Netherlands, Australia, Brazil, Denmark, Finland, France, Italy, New Zealand, Poland, Sweden, Switzerland, Turkey, Ukraine and the United States.

President Vladimir Putin said at an Arctic forum yesterday that the activists were clearly not pirates but had broken international law, which suggests they might end up facing less severe charges.

Russian freelance photographer Denis Sinyakov, who was documenting the protest, is one of those ordered to be held for two months.

Advocacy group Reporters Without Borders said Mr Sinyakov's detention was an "unacceptable violation of freedom of information".

Dozens of journalists and activists have protested outside the Investigative Committee headquarters in Moscow.

In Bulgaria, police arrested six Greenpeace activists who blocked a Gazprom gas station to protest against the Russian state-owned petrochemical giant's Arctic drilling plans.

Around a dozen Greenpeace protesters demonstrated in Hong Kong against the Russian authorities over the arrests.