Russia is still holding a Greenpeace ship despite an international court order demanding its release, the environment lobby group said Thursday.

The Dutch-flagged Arctic Sunrise ship was seized in September over Greenpeace's protest against oil drilling by Russian energy giant Gazprom.

Thirty activists, including four Russians were detained in the process, before being bailed and then benefitting from a Kremlin-backed amnesty.

The ship, however, remains under Russian control, Greenpeace said.

"Arctic Sunrise is still at the Murmansk port. Nothing has changed since last year," said Greenpeace Russia spokeswoman Tatyana Vasilyeva.

"Our lawyers are working on lifting the arrest," she said, adding that Russian officials have not set any conditions for releasing the ship.

"We don't know anything about when the ship will be freed."

The Germany-based International Tribunal for the Law of the Sea ruled in November that Russia must release the ship upon the posting of a 3.6 million euro bond.

The Netherlands then proceeded to issue a bank guarantee constituting the bond but Russia ignored the court's ruling.

The dispute recently made headlines again after Senegal seized a Russian vessel called the Oleg Naidenov for allegedly fishing illegally.

Russia then accused Senegal of acting under pressure from Greenpeace in detaining the Oleg Naidenov, whose home port is Murmansk.

Greenpeace campaigns against illegal fishing in Senegal, and has in the past used the Arctic Sunrise ship to catch vessels in the act.