A Cambodian court on Tuesday sentenced 10 environmentalists to between six and eight years in jail over their activism in a case condemned by rights campaigners as a "crushing blow" to the kingdom's civil society.

The activists from Mother Nature, one of Cambodia's few environmental advocacy groups, denied charges of plotting against the state, which they said were politically motivated.

The court sentenced the activists to jail terms ranging from six to eight years, Am Sam Ath, operations director of rights group LICADHO, said.