Greenpeace activists facing trial for a protest against Arctic oil drilling have been barred from leaving the country by Russian investigators, despite an international court ruling, the organisation has said.

In a statement on Friday, Greenpeace said that Russia's Federal Investigative Committee rejected a request for it to seek exit visas for the 26 foreign environmental activists from 17 countries who were among the 30 arrested after an attempt to scale Russia's first offshore oil platform in the Arctic in protest.

The committee "has written to one of the 30 - Anne Mie Jensen of Denmark - indicating that they are not free to leave the country", the Netherlands-based environmental group said in a statement.

"Lawyers for Greenpeace expect all of the non-Russian defendants to be treated in the same way by the authorities, meaning they would now be forced to stay in St Petersburg for Christmas and possibly well beyond," it said.

The investigative committee declined immediate comment.

The activists face up to seven years in prison on hooliganism charges, but were released on bail last month by courts in St Petersburg and hoped to be able to go home pending trial or further action by investigators that requires their presence.

The UN maritime tribunal ruled on November 22 that the Greenpeace ship and its crew must be allowed to leave Russia, but Moscow declined to take part in the case lodged by the Netherlands and has suggested it would defy the ruling.

'Unfounded charges'

Greenpeace says the protest was peaceful and the charges unfounded. The arrest of the activists, who were held in jail for two months and initially risked up to 15 years in prison on piracy charges, has drawn criticism from the West.

"We were seized in international waters and brought to Russia against our will, then charged with a crime we didn't commit and kept in jail for two months," Greenpeace quoted Arctic Sunrise captain Peter Willcox, a US citizen, as saying.

"A respected international court says we should be allowed to go home [...] but we can't get visas to leave the country," Willcox said.

Russia's Federal Migration Service has said it would not issue visas until it receives a direct request from the investigative committee, Greenpeace said.

Moscow says activists endangered lives and property in the protest at the state-controlled energy giant Gazprom's Prirazlomnaya platform in the Pechora Sea, a key element of Russia's plans to develop the Arctic.

Putin last week ordered his military to increase its focus on the resource-rich region Arctic, where Russia is vying for control with Canada, the United States, Denmark and Norway.

Production at the field served by Prirazlomnaya, Russia's first Arctic offshore oil project, is due to begin this month.

The foreign activists include citizens of Argentina, Australia, Brazil, Britain, Canada, Denmark, France, Finland, Italy, the Netherlands, New Zealand, Poland, Sweden, Switzerland, Turkey, Ukraine and the United States.