Thailand, which was forced to cancel a key Asian summit in April amid chaotic anti-government protests, has failed to reconvene the meeting next month, the prime minister admitted on Wednesday.
The government had hoped the regional meeting would finally be held in mid-June, but premier Abhisit Vejjajiva said it was now likely to be pushed back to October -- 10 months later than originally planned.
He said leaders from the 10-member Association of Southeast Asian Nations (ASEAN) and its six key regional partners had not been able to reschedule the meetings for June 13-14 on the southern tourist isle of Phuket.
"There are countries that cannot attend the meeting we proposed," Abhisit said, adding that the most likely alternative date was October, when a second ASEAN summit was already due to be held.
"I am concerned that we are unable to hold the meeting as it was due to discuss several agreements," he said.
Abhisit said senior bureaucrats from the 16 countries would discuss new dates at their own meeting on May 19 in Phuket.
"Some countries are having by-elections, two or three countries are having general elections and others have plans to host state visits that cannot be moved," Foreign Minister Kasit Piromya earlier confirmed.
"Every country has tried to make our proposed dates work but they cannot adjust schedules," he said.
The summit groups the leaders of China, Japan, South Korea, India, Australia and New Zealand, along with those of ASEAN members Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, the Philippines, Singapore, Thailand, and Vietnam.
The ASEAN Plus Six meetings were originally planned for December in Bangkok but were repeatedly moved because of demonstrations against the last administration, allied to fugitive former prime minister Thaksin Shinawatra.
Following a change in government the summit was organised in the coastal city of Pattaya. But before it began, protesters demanding Prime Minister Abhisit Vejjajiva's resignation stormed the venue on April 11, forcing its closure.
Its cancellation was a huge embarrassment for the kingdom, which invoked emergency measures for a few hours while foreign leaders were urgently ferried away.
"I am sorry... several countries feel the same was but everyone understands what happened in Pattaya," said Abhisit.
"We lost an opportunity as the meeting would have produced several economic agreements," he said.
Thailand had tried to reassure leaders that a new meeting in Phuket in June would be free of political chaos by promising to use an internal security law that placed the army in charge of guarding the summit.