Russia on Wednesday dropped all but one of the cases against 30 crew members of a Greenpeace protest ship following a Kremlin-backed amnesty.

The move marks the end of a three-month criminal probe against the 26 foreign and four Russian activists and comes less than two months before Moscow hosts the Winter Olympic Games in Sochi.

In what was widely seen as another in a series of attempts to improve Russia's battered international image ahead of the event, Kremlin critic Mikhail Khodorkovsky was also pardoned by President Vladimir Putin and flew to Germany on Friday after a decade behind bars.

On Wednesday, Russia's highest court agreed to review the two sets of convictions against Khodorkovsky, who expressed hope that his jailed business partner would soon be released too.

Twenty-five foreign Greenpeace activists were earlier in the day summoned to the Investigative Committee to receive confirmation that the hooliganism probes launched after their September protest against oil drilling in the Barents Sea had been dropped, Greenpeace said.

Only Italian activist Cristian d'Alessandro failed to receive the relevant paperwork. Greenpeace said the delay was due to the absence of a translator and the Italian was invited to return on Thursday.

Anthony Perrett of Britain was the first Greenpeace member to have his case dismissed on Tuesday.

The four Russian crew members also benefitted from the amnesty.

"The final chapter in the legal ordeal of the Arctic 30 began today," Greenpeace said in a statement.

The foreigners are expected to receive exit visas to leave Russia "in the coming days," the group said.

Five people come from countries that have a no-visa regime with Russia. But "they also need the migration service sticker to leave," said spokesman Ben Stewart.

The group said it also expected Russian investigators to release all the equipment seized during the raid of the Arctic Sunrise, as well as the ship itself, which is still impounded at Russia's northern port of Murmansk.

The icebreaker was boarded by Russian border guards and towed to Murmansk in September after several activists attempted to scale Gazprom's Prirazlomnaya oil rig.

The crew spent several weeks detained in local jails before being transferred to Saint Petersburg and released on bail. Originally facing a charge of piracy, they were later targeted with the less severe hooliganism accusation.

An international maritime court in Germany in November told Russia to release the activists and the ship in response to a formal complaint lodged by the Netherlands, under whose flag the ship sailed.

Russia boycotted the German court hearings and ignored the ruling.

On Monday, two Pussy Riot punks, Nadezhda Tolokonnikova and Marina Alyokhina, who had been jailed for two years over an anti-Kremlin protest, also walked out to freedom under the amnesty.

They had been due to be released in March.

Review of Khodorkovsky convictions

In a separate development, Russia's supreme court said that a review of both the 2005 and 2010 convictions of Khodorkovsky and his business partner Platon Lebedev would be conducted within the next two months.

"Formally, this should be reviewed within the next two months, but I think it is actually going to happen much sooner," court spokesman Pavel Odintsov told AFP.

Khodorkovsky welcomed the decision.

"I very much hope that bureacratic procedures would not be too long and allow Platon Lebedev to walk out to freedom soon," he said in a statement.

The former tycoon arrived in Berlin on Friday from his penal colony near the Finnish border after receiving a surprise pardon from Putin.

His release comes after more than two years of mediation between the Kremlin and Germany's former foreign minister Hans-Dietrich Genscher.

Khodorkovsky was jailed in 2003 and convicted in 2005 of fraud and tax evasion linked to his time as boss of the now-defunct private oil giant Yukos.

He and co-defendant Lebedev were sentenced again in 2010 on a new set of money-laundering and embezzlement charges that were brought shortly before both were set to be released.

The European Court of Human Rights ruled in July that the 2005 charges against Khodorkovsky and his business partner "had a sound basis, but the hearing of their case was unfair, and their placement in remote penal colonies unjustified".

The 50-year-old has said he will stay out of Russia for as long as the 2005 court order for him to pay $550 million in damages remained in place.