Foreign ministers of Myanmar, Laos and Cambodia and Vietnam's deputy foreign minister joined the talks hosted by Thailand's foreign minister, according to Thai foreign ministry spokeswoman Kanchana Patarachoke.
"The consultation was a non-ASEAN meeting but intended to complement ASEAN’s ongoing collective efforts to find a peaceful political resolution," Kanchana said in a statement.
Myanmar Foreign Minister Wunna Maung Lwin attended along with Kan Zaw, minister for investment and foreign economic relations, and Ko Ko Hlaing, minister for international cooperation, Myanmar's foreign ministry said in a statement.
The Philippines said its foreign minister would also not join, without elaborating.
"Any meeting convened under ASEAN, formal or informal, should not divert from this decision," it said, according to the source.