A court hearing in the case of Kremlin critic Alexei Navalny got underway at 1230 (0930 GMT) on Monday in the town of Khimki, near Moscow, his spokeswoman Kira Yarmysh said on Twitter.
Russia's prison service has asked that Navalny be held in custody, the Interfax news agency reported.
Western nations have urged Russia to immediately free Navalny, who was detained on Sunday at a Moscow airport after flying home for the first time since he was poisoned last summer.