A Russian court on Friday rejected the bail requests of two British nationals remanded in custody along with the 28 other crew members of a Greenpeace ship that protested Arctic oil drilling.

A regional court in the northern city of Murmansk turned down the appeal to release a freelance British video journalist Kieron Bryan and Greenpeace activist Phil Ball, who is also from Britain, the environmental group said.

Investigators have placed all 30 Greenpeace crew members from 18 countries in pre-trial detention for two months until late November and charged all 30 of them with piracy, which carries a maximum sentence of up to 15 years.

On Wednesday, investigators said that "narcotic substances" had been found on the ship and several more activists would face new charges.

Earlier this week the court turned down the appeal to release four crew members including freelance Russian journalist Denis Sinyakov.

Greenpeace's International Executive Director Kumi Naidoo sent a letter to Russian President Vladimir Putin, asking for a meeting and offering himself "as security" to have the activists released on bail.

Putin's spokesman Dmitry Peskov said Friday that Putin had heard of Naidoo's letter but had not received it yet, and stressed that the president could not intervene in investigations.

"He knows about it but since we haven't seen the letter yet, we can't talk about anything," Peskov was cited as saying by Interfax news agency.

Putin "can hardly be dragged into any discussion of the activities of the investigation", he added.

In an interview with AFP, Naidoo said he was "extremely surprised" by Russia's response to a Greenpeace attempt to scale a state oil rig last month.