The Pheu Thai Party claimed Wednesday the country spent more than 600 million baht in a campaign leading up to Thailand's defeat in the race for a non-permanent seat on the United Nations Security Council (UNSC).
Deputy Prime Minister Prawit Wongsuwon said the defeat to Kazakhstan did not surprise him.
"We had anticipated that," Gen Prawit said. "Never mind. Next time."
Gen Prawit was replying to a question as to how he felt after Thailand attracted the support of only 55 countries against 138 for Kazakhstan in a second round of voting at the UN headquarters in New York on Tuesday.
In the first round, the oil-rich nation won only 113 votes versus 77 for Thailand, short of the required two-thirds backing from all 193 members, or 129 votes.
Pheu Thai's former foreign minister Surapong Tovichakchaikul said the defeat was not beyond expectation as it shows how the international community has disliked Thailand's military rulers since the May 2014 coup.
"We should have withdrawn from the race right after the coup, so we could have saved face and more than 600 million baht in campaign expenses," Mr Surapong said, adding the budget was set by his government, but then spent by the military administration.
The Thai bid delegation, comprising former Asean secretary-general Surin Pitsuwan and other retired ambassadors, had been optimistic about winning the race under the "Building Bridges for Partnership: Thailand 2017-2018 Candidate for the UN Security Council" campaign.
Sources at the Foreign Ministry told the Bangkok Post among the "huge expenditure" items were first-class air tickets for special Thai envoys, free Bangkok trips for senior UN officials from New York and a reception on a cruise run by a five-star hotel for diplomats in New York.
Foreign Ministry spokesman Sek Wannamethee declined to answer repeated phone requests to comment on the cost of the campaign.
But before the Pheu Thai statement was released, Mr Sek said the campaign "has raised Thailand's profile as a prominent member of the United Nations through onsite visits to various countries and organisations under its campaign. The visits help us deepen relations with many allies, especially cooperation on trade and investment."
Thailand, which held a UNSC seat in 1985-1986, has had a long history of engagement with the UN since its admission in December 1946, hosting more than 30 regional UN-affiliated agencies in Bangkok.
But the country's international reputation has been deteriorating since the May 2014 coup. Thailand's civil and political rights indexes and rankings have been relegated to the bottom or near the bottom.
But Mr Sek dismissed the notion, saying "concerns about our politics have never been brought to the table".
Bangkok wanted to contest the seat again for the 2011-2013 period but later withdrew from the race after India declared its candidacy, Thai diplomats said.
The idea to do so again for the 2017-2018 term emerged after the 2006 coup, they said.