Defenders of Russia's most prominent rights group Memorial urged the Supreme Court on Thursday to dismiss a case to shut it down, saying the move would mark a dark day for the country.
In court for alleged violations of its designation as a "foreign agent", Memorial is facing its biggest threat since being founded by Soviet dissidents including Nobel Peace Prize laureate Andrei Sakharov in 1989.
A pillar of Russian civil society, Memorial has built up a huge archive of Soviet-era crimes and campaigned tirelessly for human rights in Russia.
Prosecutors have asked the Supreme Court to dissolve Memorial International, the group's central structure, for alleged failures to use a "foreign agent" label as required under a controversial law regulating groups that receive funding from abroad.
The move has sparked widespread outrage, with supporters saying the shuttering of Memorial would signal the end of an era in Russia's post-Soviet democratisation.
It comes in a year that has seen an unprecedented crackdown on opponents of President Vladimir Putin, including the jailing of top Kremlin critic Alexei Navalny and the banning of his organisations.
During the hearing, which lasted for several hours before being adjourned until December 14, prosecutors accused Memorial of "systematically" failing to use the foreign agent label and of trying to hide its status.
One asked Memorial co-founder Yelena Zhemkova at what point she had started putting the label on her business cards.
- 'Insult to millions' -
Memorial's lawyers and founders denied any serious violations, saying its material was properly marked and that only an insignificant number of documents may have been missing the label.
They emerged from the hearing to applause from supporters.
"We will continue to fight to prove that an organisation that has worked for 30 years to help people cannot be closed because of unfounded technicalities," Zhemkova said.
More than 200 people gathered outside the court on a cold Moscow day to support the group, some wearing black facemasks reading "Memorial Cannot be Banned".
Maria Krechetova, a 48-year-old philosophy teacher, said shutting Memorial would be an "insult to the millions" of those who suffered under the repressive Soviet regime.
"Banning Memorial would deal a final blow to the idea that a person means something (in Russia), and that their rights mean something," she said.
"Memorial plays a huge role in our country. This organisation, above all, studies history, repressions," said 18-year-old Arina Vakhrushkina.
"It is a page in our history the authorities are trying to turn and forget about, they only want to be proud of our victories."
More than 100,000 people have signed an online petition asking for the case to be dropped.
Thursday's hearing was in one of two cases brought this month against the group and is being heard by the Supreme Court because Memorial International is registered as an international body. The ruling will not be open to appeal in a Russian court.
The other case, against the Memorial Human Rights Centre, began in a Moscow court on Tuesday and will continue later this month.
- Cataloguing Soviet atrocities -
It is also accused of violating the "foreign agent" law and facing another charge of defending "extremist and terrorist activities" for publishing lists of imprisoned members of banned political or religious movements.
Memorial has spent decades cataloguing atrocities committed in the Soviet Union, especially in the notorious Gulag network of prison camps.
It has also campaigned for the rights of political prisoners, migrants and other marginalised groups and has highlighted abuses especially in the turbulent North Caucasus region that includes Chechnya.
It is a loose structure of locally registered organisations, but the dissolving of its central structure would have a major impact on operations.
Memorial International maintains the group's extensive archives in Moscow and coordinates dozens of Memorial-linked NGOs in and outside of Russia.
Memorial lawyer Grigory Vaypan said he doubted the courts would reject prosecutors' requests.
"Unfortunately, the courts in Russia are arranged in such a way that if a claim is made by state bodies, especially the Prosecutor General's office, it is very likely the claim will be satisfied."