PHNOM PENH (Reuters) - Cambodia’s Supreme Court on Monday rejected a plea for bail by detained opposition leader Kem Sokha, following his arrest last year on charges of seeking to overthrow the government.

Supporters of Kem Sokha, former opposition leader and ex-president of the now-dissolved Cambodia National Rescue Party (CNRP), hold up a poster near the Appeal Court in Phnom Penh, Cambodia, March 27, 2018. REUTERS/Samrang Pring

Kem Sokha, head of the now dissolved Cambodia National Rescue Party (CNRP), was arrested on Sept. 3 amid a crackdown on critics of authoritarian Prime Minister Hun Sen who has ruled the Southeast Asian country for more than 30 years.

Kem Sokha, who has denied the accusations against him, has been in pre-trial detention since September.

The Supreme Court on Monday rejected a request from his lawyer that he be granted bail. An Appeal Court rejected bail in February.

“The Supreme Court upheld the Appeal Court’s decision”, said lawyer Pheng Heng.

“I am not satisfied with the court decision,” he said, adding that Kem Sokha was not in good health when lawyers last visited him on April 30.

Rights groups have condemned the crackdown by Hun Sen’s government against opposition politicians, independent media and some non-governmental groups.

The crackdown comes ahead of a July 29 general election that Hun Sen is widely expected to win now that the CNRP has been dissolved and more than 100 of its lawmakers banned from politics.

Kem Sokha was accused of plotting to overthrow the government with U.S. help, an accusation both the United States and Kem Sokha have rejected.

No date has been set for his trial.