Greenpeace says investigators have dropped charges against 16 out of 30 activists who were detained in Russia's Arctic in September.
Greenpeace said on its website on December 25 that Russian authorities were in the process of dropping charges against the remaining detainees.
On December 24 Russian authorities notified oneof those held that his criminal case was closed.
The remaining 29 activists were summoned to receive similar notifications on the following day.
The news comes less than a week after the Russian legislature passed an amnesty that has already freed several other high-profile inmates whose cases were criticized as politically motivated.
Thirty crew members and environmentalists aboard the "Arctic Sunrise" ship were detained after security forces in September raided and seized the vessel, a Greenpeace icebreaker carrying activists who had scaled a Gazprom offshore oil rig in the Pechora Sea to protest oil drilling above the "ice line."
The detainees, which included Russians and citizens of 15 other countries, were released on bail last month but not allowed to leave Russia.
Russian officials initially charged them with "piracy" before then suggesting they would seek lesser charges of "hooliganism."
The case has caused friction between Russia and the Netherlands, where the "Arctic Sunrise," which has a history of peaceful environmental protests, is registered.
In addition to Russians, the detainees include nationals from Brazil, Canada, Italy, Argentina, Poland, New Zealand, Ukraine, Turkey, the United States, the United Kingdom, Australia, Sweden, Switzerland, France, Finland, the Netherlands, and Denmark.
Gazprom announced just a few days ago that it had begun commercial production of oil from that drilling platform in the "Prirazlomnaya" oil field, which Greenpeace and other opponents claim is a major threat to the pristine Arctic environment.
Greenpeace warned in a statement
that the drilling development means the "'clock is ticking' on a major environmental accident in the Arctic region."
WATCH: Russian authorities raided the Greenpeace offices following the detentions:
The dropping of the Greenpeace charge follows surprise releases in three other major cases in Russia -- including the pardon of jailed former Yukos executive Mikhail Khodorkovsky and the amnestying of two jailed activists of the punk-rock collective Pussy Riot.
All had been openly critical of President Vladimir Putin and served the majority of their prison sentences.
Many observers speculate that Russian officials -- already under fire over antigay legislation and attacks on the lesbian, gay, bisexual, and transgender (LGBT) community as well as other perceived rights offenses -- are effecting the releases to improve their image ahead of the Winter Olympics in the Russian Black Sea resort of Sochi in February.
With Kremlin backing, Russian lawmakers last week passed an amnesty that cleared the way for the releases of Khodorkovsky and Pussy Riot activists Nadezhda Tolokonnikova and Maria Alyokhina.
All have since decried the situation in Russia, with Tolokonnikova calling the amnesties "laughable"
and urging a boycott of the Sochi events.
A number of major international leaders -- including the U.S. and German presidents -- have announced their decision to stay away from the Sochi Olympics.
Based on reporting by AP, AFP, BBC, and RFE/RL