A St. Petersburg opposition leader has been handed an unexpectedly harsh 14-day sentence for staging a banned rally and disobeying police orders, an opposition spokeswoman said Wednesday, in the latest sign of a state crackdown on dissent.

Andrei Pivovarov was jailed by a St. Petersburg district court Tuesday for his actions during an opposition event on Aug. 31, his colleague Yelena Dikun said.

Pivovarov heads the local branch of the Russian People's Democratic Union, a political vehicle for former prime minister-turned-opposition activist Mikhail Kasyanov.

"This is an unprecedented case. No one has been arrested in Russia for such a long term for taking part in a political event," Dikun, a spokeswoman for the group, said by telephone.

The court also fined Pivovarov 2,000 rubles ($65), Kasparov.ru reported.

Prominent lawyer Genri Reznik called the punishment "too harsh for this kind of violation," saying in an interview with Ekho Moskvy radio that the court should have only fined Pivovarov.

Pivovarov's lawyer has appealed his conviction while supporters from his group as well as Yabloko, Solidarity and Oborona staged a series of one-person pickets outside his detention facility Wednesday.

"The union considers Pivovarov's arrest yet another proof that authorities want to silence the people," Dikun said.

The August rally was part of a series of regular protests that opposition and human rights activists try to stage in major cities on the last day of every 31-day month to draw attention to Article 31 of the Constitution, which grants freedom of assembly. Authorities have turned down most requests for these rallies, held since July 2009.

Human rights champion Lev Ponomaryov, 69, was jailed for four days last weekend on the same charges as Pivovarov at a separate, unsanctioned opposition rally in Moscow on Aug. 12. Previously, activists staging banned rallies usually got off with moderate fines.

Moscow prosecutors also opened a series of checks into the paperwork of leading rights groups this week in what analysts said could be a warning from the authorities to their critics.

The crackdown comes even as authorities try to improve their record on democracy through the Civil Society Working Group, a commission led by Kremlin first deputy chief of staff Vladislav Surkov and U.S. President Barack Obama's top Russia expert, Michael McFaul.

McFaul and Undersecretary of State William Burns planned to meet with Ponomaryov in Moscow last week but could not because of his jailing. The U.S. officials expressed disappointment over the incident.

The Civil Society Working Group held its first session in Washington in January, focusing on corruption and child adoptions, and met again in May in the city of Vladimir for talks about prisoners' and migrants' rights.