He told AFP on Friday that the trials "began under tight security without journalists or rights defenders being informed" in Karshi, a town in southern Uzbekistan about 170km (105 miles) from the border with Afghanistan. Karshi is near an airbase used by government forces.
The defendants are accused of terrorism, extremist activity and infringing the constitutional order, but it was unclear whether the charges were related to a string of explosions and shootings which left at least 47 people dead early this year, Korayev said.
Fifteen other people who went on trial said their confessions were extracted under torture.
Korayev said that at least one defendant in the Karshi trials had alleged that he too was tortured while in custody.
Campaigners such as the New York-based Human Rights Watch have criticised the harshness and lack of impartiality in the courts under the government of President Islam Karimov and have estimated that about 6000 people are imprisoned on political or religious grounds.
Two years ago, a United Nations rapporteur said torture by the security forces in Uzbekistan was systematic.