By Panu Wongcha-um and Orathai Sriring

BANGKOK (Reuters) -Thailand's caretaker government hosted the foreign minister of Myanmar's ruling junta at informal regional peace talks on Sunday, as key Southeast Asian counterparts stayed away from the meeting that has drawn sharp criticism.

Only Cambodia has so far officially confirmed it intended to attend the talks.

Myanmar's generals have been barred for nearly two years from senior-level meetings of the Association of Southeast Asian Nations (ASEAN) for failing to honour an agreement to start talks with opponents linked to the ousted civilian government that had been led by now-jailed Nobel laureate Aung San Suu Kyi.

But Thailand, whose prime minister himself first took power in a military coup, invited Myanmar's junta-appointed Foreign Minister Than Swe to the talks along with other foreign ministers in the 10-member ASEAN bloc, two sources with knowledge of the meeting told Reuters.

Myanmar's junta spokesman could not be reached for comment on Sunday.

Thailand's foreign ministry was tight-lipped about exactly who was attending the two-day gathering in the resort town of Pattaya, for which outgoing Foreign Minister Don Pramudwinai sent invitation letters just four days before its start.

Don told the local news outlet Matichon on Sunday the unofficial initiative was meant to complement, not replace, ASEAN-led efforts and members were free to attend or not.

“The current situation has changed a lot. There is now more fighting within Myanmar," he was quoted as saying. "Myanmar also has a roadmap leading to elections... These things have given us the need to continue our interactions with Myanmar."

Myanmar has been roiled by violence since a Feb. 1, 2021 coup, with the military battling on multiple fronts to try to crush an armed pro-democracy resistance movement formed in response to the crackdown. The junta says it is fighting terrorists who aim to destroy the country.

'SECRETIVE INITIATIVE'

Critics of Thailand's initiative say it risks legitimising Myanmar's military government and is inappropriate because it is outside the official ASEAN peace initiative, known as the "five-point consensus".

Others questioned why Thailand called the talks now, when it is expected to have a new government in August after the pro-military coalition was soundly beaten in May 16 elections by progressive and populist parties.

Cambodian Foreign Minister Prak Sokhonn was to attend the meeting, his government said in a statement on Friday.

Other ASEAN members have declined Thailand's invitation, including this year's chair, Indonesia, as well Singapore, whose foreign minister, Vivian Balakrishnan, said on Friday "it would be premature to re-engage with the junta at a summit level or even at a foreign minister level".

Nantiwat Samart, secretary to the Thai minister of foreign affairs, defended the talks on Sunday, saying Myanmar should not be completely isolated or cut out from ASEAN, according to the Thai-language website of Nation TV.

Vietnam's government said its foreign minister would not attend "due to a prior engagement".

Malaysia also would not be attending, said two sources with knowledge of the matter. The Philippines, which did not respond to questions over the weekend, is seen as firmly in the camp of isolating Myanmar's generals.

Myanmar's opposition National Unity Government, made up of loyalists to Suu Kyi's ousted administration, condemned the Thai initiative.

"Inviting the illegitimate junta to this discussion will not contribute to the resolution of Myanmar's political crisis," it said in a statement on Saturday.

A group of 81 Myanmar activist groups released an open letter on Sunday condemning the "secretive initiative", saying it was in "blatant contradiction" with ASEAN's policy of excluding junta officials to high-level meetings.

"We demand the caretaker Thai government cancel this meeting immediately," the letter said.

(Reporting by Panu Wongcha-um and Orathai Sriring in Bangkok; Additional reporting by Phuong Nguyen in Hanoi, Rozanna Latiff in Kuala Lumpur, Ananda Teresia and Stefanno Sulaiman in Jakarta, Poppy McPherson and Devjyot Ghoshal in Bangkok and Shoon Naing; Writing by Kay Johnson; Editing by William Mallard)