Cambodia's Supreme Court on Tuesday authorized the continued detention of opposition leader Kem Sokha, who faces treason charges that critics have denounced as part of a ruling party campaign to crush political rivals before elections next year.

Sam Sokong, a lawyer for Sokha, said the Supreme Court upheld a lower court's refusal of bail on the grounds that Sokha's release would be detrimental to national security and his own safety. Sokha was not at the court hearing.

He was arrested Sept. 3 on charges of conspiring with the United States to topple the government of long-ruling Cambodian strongman Hun Sen and faces up to three decades in prison if convicted.

Sokha and the U.S. Embassy in Phnom Penh say the accusations are false.

Rights groups and Western governments are concerned by Hun Sen's increasingly draconian measures against the media and opposition. But their ability to exercise a restraining influence has been undermined by China's greater role in Cambodia, including investment and generous financial aid.

On Nov. 16, the Supreme Court will start hearing a case that seeks the dissolution of Sokha's Cambodia National Rescue Party, the only opposition party with seats in Cambodia's parliament.