PHNOM PENH, Cambodia (AP) — A Cambodian appeals court on Tuesday denied bail to opposition leader Kem Sokha on a treason charge widely seen as part of the government's crackdown on the media and political opponents before next month's elections.

Tuoch Tharith, a court spokesman, said 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 dissolution of the major opposition party was linked to the treason charge against Kem Sokha, for which he could be sentenced to up to 30 years in prison.

His lawyer Chea Cheng said they will discuss whether to attempt another appeal.

Kem Sokha was arrested on the basis of videos from several years ago showing him at a seminar where he spoke about receiving advice from U.S. pro-democracy groups. The Cambodia National Rescue Party has denied the treason allegation, saying it is politically motivated.

Cambodia's opposition has faced an onslaught of legal challenges from Hun Sen's government with the support of the courts, which are generally seen as favoring his ruling Cambodian People's Party.

Court rulings forced Sam Rainsy, Kem Sokha's predecessor as opposition leader, to remain in exile to avoid prison. Other top opposition party leaders fled Cambodia after Kem Sokha's jailing and the party's dissolution.

The government also intensified restrictions on civil society groups and independent media outlets, all but ensuring that Hun Sen will face no serious challenge at the polls.