International rights groups issued an “urgent appeal” this week for the release of three environmental activists in Koh Kong province imprisoned in August over their anti-sand dredging activities.

The Observatory for the Protection of Human Rights Defenders – a joint program of the International Federation for Human Rights and the World Organisation Against Torture – expressed concern at the “continued harassment” of detained environmentalists Sim Somnang, Tri Sovikea and San Mala, who are all affiliated with local NGO Mother Nature.

“The Observatory strongly condemns the ongoing harassment against Mother Nature, in particular the arbitrary detention and judicial harassment of [the trio] which only aim at sanctioning their legitimate human rights activities,” it said in a statement on Monday, following further questioning of the group last week at the Koh Kong court.

“The Observatory calls on the Cambodian authorities to release them immediately and unconditionally, and drop all charges against them.”

The men have been detained alongside another prominent activist who was jailed last month for alleged forest crimes.