A Russian judge refused Monday to free Australian Greenpeace activist Colin Russell, who was among 30 people arrested following a protest against oil drilling in the Arctic, signaling that others also could be kept in jail for three more months pending trial.

In a subsequent hearing, however, a judge agreed to free a Russian doctor who was on the Greenpeace ship when it was seized by the Russian coast guard on Sept. 18. Yekaterina Zaspa was released on bail of 2 million rubles ($61,500).

Investigators had asked St. Petersburg courts to extend the detention period of all 30. Hearings were scheduled Monday for seven of the group.

During similar hearings two months ago on whether to jail the defendants, the rulings were the same in all 30 cases, which made Monday's release of the Russian doctor unexpected.

The Russians arrested everyone on board the ship, including cooks and journalists documenting the protest, after a few of the environmental activists tried to scale an offshore drilling platform owned by Russian state energy giant Gazprom.