MOSCOW (AFP) -- Russia was on Wednesday dropping most of the cases against 30 Greenpeace crew members of an Arctic protest ship, marking the "final chapter" of a three-month criminal probe, the environmental group said.

Twenty five foreigners were summoned to the Investigative Committee where they expect to receive confirmation that the hooliganism probes launched after their September protest against oil drilling in the Barents Sea are dropped, Greenpeace said.

"The final chapter in the legal ordeal of the Arctic 30 began today as the group was asked to attend a meeting at Russia's powerful Investigative Committee, where the criminal case against them is being dropped en masse," Greenpeace said in a statement.

The move is part of a Kremlin-backed amnesty that specifically mentioned the charge of hooliganism that covers the environmental campaigners, whose detention sparked global protests and tainted Russia's image ahead of February's Winter Olympic Games in Sochi.

The documents will allow the foreigners to seek exit visas in order to leave Russia, concluding a saga that started when the ship Arctic Sunrise was boarded by Russian border guards and towed to a Russian port.

"The Arctic 30 are expected to leave Russia in the coming days," Greenpeace said in a statement, referring to the foreigners among the crew.

By Wednesday afternoon, several foreign Greenpeace activists had documents proving the prosecution against them has been halted, Greenpeace said. One, British national Anthony Perrett, had his case dropped Tuesday.

The four Russian nationals are also expected to benefit from the amnesty.

The crew of 28 activists and two journalists, which included 26 foreign nationals, spent almost two months in detention, first in northern Murmansk and then in Saint Petersburg.

They were freed last month on bail, and were not allowed to leave, with migration officials requiring a green light from investigators on the case.

The news Wednesday was met with relief, with the US captain of the ship Peter Willcox saying he was "pleased and relieved the charges have been dropped."

Russia's state-owned energy giant Gazprom, whose Prirazlomnaya rig was the target of the Greenpeace protest, last week announced that it had started oil production at the platform.