The Russian Supreme Court ruled that the Jehovah's Witnesses are an "extremist" group.
The group, which has vowed to appeal the verdict, was earlier declared an extremist organization by a Moscow city court in January, state media reported.
"The treatment of the Jehovah's Witnesses reflects the Russian government's tendency to view all independent religious activity as a threat to its control and the country's political stability", Thomas J. Reese, S.J., chairman of the USCIRF, said.
Koretskaya said she had been expelled from the religious organisation and its members had been banned to communicate with her after she started close but officially unregistered relationship with a man.
Interfax news agency quoted Sergei Cherepanov, a Jehovah's Witnesses representative, as saying that the group will appeal the decision in the European Court of Human Rights. But Russian authorities repeatedly targeted the group in a wide-ranging crackdown on religious freedom.
"We will do everything possible", he said. They also reject military service and blood transfusions.
The Supreme Court ruling, which followed six days of hearings, marks the first time Russian Federation has banned an organized religious organization, according to the United States Commission on International Religious Freedom (USCIRF).
Its members are known for preaching on doorsteps, where they offer religious literature and attempt to convert people.
Leaders of the group could face as many as 10 years in prison.
Jehovah's Witnesses has more than 8 million adherents worldwide, but the group stands apart from key aspects of Christian doctrine as practiced by Roman Catholics and numerous Protestant denominations.
The Moscow branch at the time had been accused of breaking up families, inciting its members to suicide and endangering their lives and health by not allowing its members to have blood transfusions.