MOSCOW — Thousands of opposition supporters gathered Saturday outside the old KGB headquarters in central Moscow to mark a year of mass protests against Vladimir Putin and his government.

The turnout was far smaller than the tens of thousands who filled Moscow streets in protests that erupted after fraud-plagued parliamentary elections last December. But unlike most of those protests, Saturday's gathering was not authorized and those who came risked arrest and heavy fines.

Soon after Putin returned to the presidency in May, Russia passed a law raising the fine for participating in unauthorized rallies to the equivalent of $9,000, nearly the average annual salary.

Even if the protest had been authorized, the opposition would have struggled to draw a crowd. Enthusiasm for street demonstrations has waned, in part because of disillusionment with the opposition leaders, while polls show that discontent with Putin's government has continued to rise.

Police dispersed the rally after 21/2 hours. Several prominent opposition figures were among dozens detained in the course of the gathering, but all were released within hours.

There was a heavy police presence around the approximately 3,000 people who came to Lubyanka Square for the rally. The square is outside the headquarters of the Federal Security Service, the main successor agency of the Soviet KGB.

The square also holds the Solovetsky Stone, a monument to the victims of political repression during the Soviet era. The stone comes from the Solovestky archipelago, the site of early prison camps considered the beginning of the Gulag system.

Many rally participants laid flowers at the stone, among them Boris Nemtsov, a veteran Russian politician now in the opposition.

"The people who have come here are free, honest and decent people," Nemtsov said "I'm very proud of our people."