Updated

A court in Cambodia on Thursday extended by six months the pre-trial detention of Kem Sokha, the leader of the now-dissolved main opposition party who already has been held for a year on a treason charge.

One of Kem Sokha's lawyers, Chan Chen, said the court ruled in a closed-door hearing that his continued detention was necessary for national security and further investigation. The hearing was held at Trapeang Phlong prison in the eastern province of Tboung Khmum, where Kem Sokha is being held.

There were hopes among his supporters that he might be released because in the past two weeks more than 20 people imprisoned for political activities have been freed with pardons or on bail. Their releases came after Prime Minister Hun Sen's ruling Cambodian People's Party won July's general election, sweeping all 125 National Assembly seats.

Kem Sokha was arrested last September on the basis of several-year-old videos showing him at a seminar where he spoke about receiving advice from U.S. pro-democracy groups. His opposition Cambodia National Rescue Party denied the treason allegation, calling it politically motivated. Another court last November dissolved the opposition party, saying it was plotting with U.S. assistance to overthrow Hun Sen's government.

Cambodia's courts are considered to be heavily politicized and under the influence of Hun Sen's ruling party. The Cambodia National Rescue Party presented the only viable political opposition, so its elimination from July's polls ensured a landslide victory for Hun Sen.

On Wednesday, Hun Sen said publicly that Kem Sokha would not be released and would not receive a pardon because he has not yet been convicted.