Asian pro-democracy and human rights groups have called on Asean member states to intervene to reverse Cambodia’s “severe deterioration” into political instability, adding it was not too late to reinstate the opposition and hold legitimate elections.

As the 32nd Asean summit kicked off in Singapore on Wednesday, Human Rights Watch, the Asian Network for Free Elections and other groups called on Singapore Foreign Minister Vivian Balakrishnan to urge Cambodia to change course after the “severe deterioration in the state of human rights and democracy”.

Last year, the opposition Cambodia National Rescue Party – the nation’s only viable opposition – was dissolved and its leader, Kem Sokha, was arrested on charges of “treason”.

The increasingly repressive steps were “in disharmony” with Asean’s core principle to “promote regional peace and stability through abiding respect for justice and the rule of law”, the letter reads.

“It is not too late for the Cambodian government to restore a fair environment for the July 29, 2018 national election, which will allow the Cambodian people to choose their leaders in a credible electoral process,” it says. “No Cambodian government elected under the current circumstances would have any claim to legitimacy.”

Exiled former CNRP Deputy President Mu Sochua said what Prime Minister Hun Sen needed most was legitimacy, “which he won’t have if he competes alone”.

Foreign Ministry and government spokesmen could not be reached, but in the past the government has argued that Asean must abide by the principle of “noninterference”.