
The planned meeting in Phuket has been postponed to the end of October.
The Abhisit government has cited busy schedules of other heads of states. But sceptics believe unsettled political trouble in Thailand might be the main reason.
Foreign Minister Kasit Piromya announced the postponement from the middle of next month to late October.
He told reporters that many government leaders of several countries found the June schedule to be inconvenient.
The decision to postpone the summit yet again followed a news report two days ago that foreign leaders were still feeling uneasy about political trouble in Thailand.
They witnessed the kingdom's problems first-hand when anti-government protesters forced cancellation of their meeting in Pattaya on April 11.
The report said some foreign leaders were pondering bringing their own guards to the planned June summit.
This has unsettled the Thai government, with Army chief Anupong Paochinda reportedly saying that presence of foreign guards could affect Thailand's image and reputation.