Prime Minister Lee Hsien Loong in a video call on Friday urged the regional group's new chair, Cambodia, to engage all sides in Myanmar's conflict, Singapore's foreign ministry said on Saturday.
Lee told his Cambodian counterpart Hun Sen that ASEAN should continue inviting a non-political representative from Myanmar to its meetings and any decision to change that "had to be based on new facts".
His remarks follow a controversial visit last week by Hun Sen to Myanmar, where he met Min Aung Hlaing, the head of the military government whom ASEAN excluded from its leaders' summit for his failure to implement the five-point plan to end hostilities and allow dialogue after a coup last year.
Malaysia's foreign minister, Saifuddin Abdullah, made similar comments on Thursday, saying some ASEAN members felt Hun Sen should have discussed his trip with fellow leaders beforehand, as it could be seen as recognising the junta.
Lee told Hun Sen any engagement with Myanmar needed to include "all parties concerned", including Nobel laureate Aung San Suu Kyi's ousted ruling party.
The Singapore leader said that despite Myanmar's peace commitments, the military has made further attacks against its political opponents and imposed further prison sentences on Suu Kyi.
Hun Sen made some proposals to Lee on how to coordinate a ceasefire in Myanmar and deliver humanitarian assistance, according to the statement. Lee responded these could be complicated because there had been no access to all parties, although Singapore did not object to the idea in principle.
All of Cambodia's proposals, as ASEAN chair, should be further discussed among ASEAN foreign ministers, Lee said, according to the statement.
"Prime Minister Lee hoped that Cambodia would consider his views and those of other ASEAN leaders," it said.
Cambodia on Wednesday postponed the inaugural meeting of its ASEAN chairmanship, scheduled for next week, because some foreign ministers had expressed "difficulties" in attending.
Lee's remarks also come days after Cambodian Foreign Minister Prak Sokhonn said on his Facebook page that Singapore backed Cambodia's approach on the Myanmar crisis.
(Reporting by Aradhana Aravindan; Editing by Martin Petty and William Mallard)