There has been no indication whatsoever that the junta will take serious steps to implement ASEAN’s five-point consensus.
Hun Sen also urged Japan to step in by joining a group called “Friends of Myanmar” organised by 2021 ASEAN chair Brunei.
Nobel laureate Suu Kyi, 76, is on trial in nearly a dozen cases that carry combined maximum sentences of more than 100 years in prison.
He made the remarks during his visit to Myanmar in a bid to end the ongoing crisis and bring the country back to future ASEAN summits.
Some rights groups have made statements critical of the visit, saying Hun Sen was risking a rupture among ASEAN member states.
Cambodia Prime Minister Hun Sen will visit Myanmar on Friday and Saturday in an effort to defuse the crisis.
The massacres and burnings also signal a return to practices that the military has long used against ethnic minorities.
The international community has expressed shock over the attack with the US embassy in Myanmar describing it as "barbaric".
Photos showed the charred bodies of over 30 people in three burned-out vehicles.
Aung San Suu Kyi is also charged with multiple counts of corruption and violating the official secrets act.