Former chess champion Garry Kasparov was convicted of leading an opposition protest and sentenced to five days in jail by a Moscow court Saturday.
Kasparov and dozens of other demonstrators were detained hours earlier after riot police clashed with Kremlin opponents following a protest rally that drew several thousand people.
The former chess champion was forced to the ground and beaten, his assistant Marina Litvinovich said in a telephone interview from outside the police station where Kasparov was held.
"What you've heard is all lies," Kasparov said after the sentence was read. "The testimony is contradictory. There was not a single word of truth."
Two riot police testified in court that they had been given direct orders before the rally to arrest Kasparov, one of President Vladimir Putin's harshest critics. One of the policemen acknowledged that the two reports he had filed were contradictory.
Kasparov was charged with organizing an unsanctioned procession "of at least 1,500 people directed against President Vladimir Putin," of chanting anti-government slogans and of resisting arrest.