The US wanted the declaration to be signed during President Trump's visit, he said in connection with Monday's meeting with the Association of Southeast Asian Nations (ASEAN).
The statement comes as Thailand and Cambodia agree to hold new talks on Wednesday.
Sometimes we need to sit down and discuss properly so that what we agree on really holds true, says Sihasak Phuangketkeow.
The current unrest has been ongoing since May and ceasefires have been agreed twice since then, but did not hold, most recently in October, when Donald Trump led the signing ceremony on site at the ASEAN summit in the Malaysian capital Kuala Lumpur.
But despite the American president's efforts, fighting resumed in November.
Sihasak Phuangketkeow emphasizes that expectations for the new talks are not the highest:
Our position is that a ceasefire does not come with an announcement, but must come from action.
Dozens of people have been killed and hundreds displaced on both sides of the border in recent weeks.
