The Investigative Committee has applied to extend the detention period of the 30 people held in connection with a protest against oil drilling in the Arctic in September, Greenpeace Russia said.
In a statement on its website Friday, Greenpeace Russia said investigators had already filed six applications to extend the activists' detention period with St. Petersburg's Kalininsky District Court, and another nine applications were expected to be filed Monday.
There was no corresponding statement of this on the Investigative Committee's website.
The head of Greenpeace International, Kumi Naidoo, said Greenpeace lawyers would appeal the extension.
"We will fight this absurd attempt to leave innocent people behind bars. If the court grants the extension, we will immediately send an appeal with demands to free the activists," Naidoo said in a statement posted on the organization's website.
The statement went on to slam the investigation into the activists as "farce and mockery of the judicial system," saying investigators had already spent two months "investigating crimes that never took place."
Twenty-eight activists and two journalists were detained after taking part in a protest near a Gazprom-owned oil platform, the Prirazlomnaya, in the Arctic on Sept. 19.
Armed Russian coastguards forcibly boarded the Greenpeace's Arctic Sunrise after the activists tried to place a Greenpeace banner on the Prirazlomnaya.
The detained activists now face hooliganism charges, and some of them may face charges of resisting arrest.
The case has attracted international attention, with many Western figures urging President Vladimir Putin to let the activists go.
Most recently, ex-Beatles star Paul McCartney sent Putin such an appeal.
The Kremlin human rights council has also written a letter in defense of the activists, calling on Investigative Committee head Alexander Bastyrkin to consider releasing them until trial, said Mikhail Fedotov, head of the presidential human rights council.
