Agreed in April last year, the plan calls for an immediate end to violence and dialogue between the army and coup opponents.
"If more prisoners are to be executed, we will be forced to rethink our role vis a vis ASEAN's five-point consensus," Cambodian prime minister Hun Sen said as he opened the foreign ministers' gathering.
Hun Sen said the bloc was "disappointed and disturbed by the execution of these opposition activists despite the appeals from me and others for the death sentences to be reconsidered for the sake of political dialogue, peace and reconciliation".
Malaysia, which has led efforts to get tough on Myanmar's junta, told reporters there must be progress before the ASEAN leaders summit in November.
"If there is no progress, then the leaders will have to ask the hard questions when they meet in November," said Malaysian foreign minister Saifuddin Abdullah, adding that suspending Myanmar from the regional bloc was not off the table.
He also described the Myanmar executions -- which came despite personal appeals from Hun Sen -- akin to "a slap".
"They are making a mockery of the five-point consensus, there is no respect to the ASEAN leaders, there is no respect to the ASEAN chair," he told reporters.
His comments were echoed by Indonesia's Retno Marsudi, who said there was "no significant progress".
"There's no goodwill and no commitment from the junta to implement the five-point plan," the foreign minister told reporters.
She added certain countries were frustrated by "broken promises" by the junta, and Hun Sen told foreign ministers that "ASEAN shouldn't be held hostage to Myanmar".
But with no representatives from Myanmar present for the summit -- highlighted by the country's prominently placed empty chair -- Cambodia's ASEAN spokesman admitted Tuesday that progress over the conflict might be tricky.
The February coup has left Myanmar in disarray, with the death toll from a brutal military crackdown on dissent passing 2,100, according to a local monitoring group.