A Cambodian appeals court has denied bail to opposition leader Kem Sokha who faces a treason charge widely seen as part of the government's crackdown on the media and political opponents.

Tuoch Tharith, a court spokesman, said Tuesday it upheld a lower court's decision that Kem Sokha must remain in pre-trial detention because the investigation into his case is still underway. It was the fourth time he'd been denied bail since being arrested in September.

Rights groups say Prime Minister Hun Sen has crippled opponents ahead of general elections in July. Kem Sokha's Cambodia National Rescue Party was dissolved in November by a court ruling.

The party's dissolution was linked to the treason charge against Kem Sokha, for which he could be sentenced to up to 30 years in prison.