Russia has dropped piracy charges against 30 Greenpeace activists, replacing them with hooliganism charges, according to officials.
The new charge has a maximum penalty of seven years rather than 15. Greenpeace says it is still "wildly disproportionate".
Greenpeace's Arctic Sunrise vessel was seized by Russian forces as activists tried to scale an offshore oil platform.
All 30 people on board were detained.
Two of them are freelance journalists.
So far all bail applications in the case have been refused.
Vladimir Markin, the head of Russia's main investigating agency the Investigative Committee, told Russian news agencies that the charges had been reclassified.
But the investigators did not rule out more serious charges at a later date - in particular the use of violence against officials.
The refusal of the detainees to give evidence also gives the authorities reason to consider other offences such as terrorism and espionage, Mr Markin said.
Last week, 11 Nobel prize-winners wrote to Russian President Vladimir Putin, urging him to drop the charges of piracy.
The presidential press secretary, Dmitry Peskov, said the president had no power to influence the courts.
Mr Putin said last month that the activists had violated international law but it was "absolutely evident that they are, of course, not pirates".
Vladimir Chuprov of Greenpeace Russia said that there was no case for either piracy or hooliganism charges.
"The Arctic 30 are no more hooligans than they were pirates," he said in a statement.
"This is still a wildly disproportionate charge that carries up to seven years in jail. It represents nothing less than an assault on the very principle of peaceful protest."
Earlier Greenpeace Russia programme director Ivan Blokov told the Interfax news agency he was surprised the Russian government had refused to attend international court hearings in Germany over the detentions.
The Netherlands took the case of the Dutch-flagged ship and its crew to the UN tribunal in Hamburg on Monday.
The Russian foreign ministry released a statement pointing out that Moscow had opted out of UN Law of the Sea dispute procedures, which infringe upon sovereignty, in 1997.
All 30 people who were on board the ship are in pre-trial detention in the northern port city of Murmansk until late November. They have complained of being held in harsh conditions,
They were detained when Russian security sources stormed the ship five weeks ago following a protest against drilling for oil in the Arctic.
Greenpeace denies any wrongdoing and is calling for the release of the detainees, who come from 18 countries, and the Arctic Sunrise.