ELEVEN opposition activists were handed down lengthy prison sentences on Tuesday for their roles in a protest at Phnom Penh’s Freedom Park last year that turned violent and left dozens injured.

In a decision that will come as a surprise to many, Judge Lim Makaron ruled that the Cambodia National Rescue Party members were guilty of taking part in an “insurrection” by attending a demonstration led by CNRP lawmakers at the public square on July 15, 2014.

“Eleven activists were sent to jail after the lawyers boycotted the trial today," Sam Sokong, lawyer for the defence, said after the ruling.

Meach Sovannara, the head of the CNRP’s information and media department, was convicted of “leading an insurrection” and sentenced to 20 years. CNRP activists Oeur Narith and Khin Chamroeun, the president of the party’s youth wing, received the same sentence.

Eight other party activists were sentenced to seven years for joining the “insurrection”.

Observers have long asserted that the case of the most prominent member of the group on trial, Sovannara, was being used by the ruling Cambodian People’s Party to exert pressure on the opposition during the long negotiations over new laws governing elections.

In April, the activist was released on bail just hours after the formation of the new National Election Committee – a key part of the negotiations – leading some to express optimism that the case was to be thrown out amid a “culture of dialogue” between Prime Minister Hun Sen and CNRP president Sam Rainsy.

Thirty-nine security personnel and at least six protesters were injured when opposition demonstrators attacked a group of notoriously violent Daun Penh district security guards at the July protest.