A group of 11 Cambodian opposition members and activists were jailed on insurrection charges Tuesday, a defence lawyer said, including three who received a 20-year sentence.

Those jailed are from the opposition Cambodian National Rescue Party (CNRP) and were arrested during clashes with the government in July 2014 against the closure of Phnom Penh's main designated protest site.

"This is a very serious sentencing. We lawyers cannot accept these convictions," Sam Sokong, the group's defence lawyer told AFP, adding his eight other clients received seven years in jail.