PHNOM PENH, Cambodia — Cambodia’s imprisoned opposition leader was denied bail by the Supreme Court on Wednesday, disappointing supporters who had hoped he might be freed now that the country’s widely criticized elections are over.

Kem Sokha, leader of the outlawed Cambodia National Rescue Party, has been held without trial for nearly a year, accused of treason. He is in solitary confinement in a remote prison near the Vietnamese border.

Several Cambodian activists and journalists have been released from prison in recent days, which led some supporters to hope that Mr. Kem Sokha would be next. Many saw the releases as an attempt by the government to burnish its reputation after the July 29 national election, in which the party of the authoritarian prime minister, Hun Sen, won all 125 seats in Parliament.

During the lead-up to the election, Mr. Hun Sen presided over a crackdown on dissenting voices and independent media. Mr. Kem Sokha was arrested on Sept. 4, accused of conspiring with the United States to bring down the Cambodian government. As evidence, prosecutors submitted an old video in which he described getting advice from Americans on building a political movement.