MOSCOW — Prosecutors on Friday said they would seek a 10-year prison sentence for Aleksei A. Navalny, Russia’s most prominent critic of President Vladimir V. Putin, on embezzlement charges that critics say are intended to crush the opposition.

At a courtroom in central Moscow, prosecutors accused Mr. Navalny and his brother, Oleg, of stealing almost $500,000 from two firms, one of which is an affiliate of the French cosmetics company Yves Rocher. Prosecutors requested an eight-year sentence for Oleg Navalny.

The judge in the case, Yelena Korobchenko, said later that she would announce the verdict on Jan. 15.

Local reporters described the men as “in shock” after hearing about the length of the requested prison terms. Aleksei Navalny denied any guilt and cited testimony from Yves Rocher employees who said that no crime had been committed.