Suriyasai Katasila, a spokesman for the People's Alliance for Democracy read from an open letter addressed to Prime Minister Thaksin Shinawatra, saying "The day the prime minister publicly and officially announces his resignation will be the day we stop protests".
Thaksin's critics dismissed his reconciliation committee proposal as insincere, with Abhisit Vejjajiva, the head of the main opposition Democrat Party, saying that if Thaksin wanted to end conflicts in the country then he should resign as soon as possible.
With official election results for Sunday's election still pending, Thaksin's rivals called on supporters - who for two months have been staging rallies drawing as many as 100,000 people - to resume protests in Bangkok as of Friday.
Thaksin had previously said he would step down if his party won less than 50% of the vote; on Monday he said he had won 57%, and saw no reason to resign, although the 16 million votes were substantially less than the 19 million his party won last year.
However, Thaksin acknowledged a strong protest vote, and said he would address accusations of corruption and abuse of power by letting an independent committee decide whether he should step down.
"If that committee tells me to quit, then I will quit"
Thai prime minister
The proposed committee would comprise three former prime ministers, three former Supreme Court chiefs and three former heads of Parliament to judge whether he should resign.
"If that committee tells me to quit, then I will quit," Thaksin said.
About 10 million voters showed their disapproval of Thaksin by casting abstention votes.
The boycott left 38 constituencies undecided, because the sole candidate in each race failed to win a required 20% of the vote, according to the unofficial results.
"This is unprecedented in Thai politics," one commission official said of the prospect of Thailand being cast into political limbo for months.
Simmering public anger against Thaksin erupted in late January after his family sold its holding in telecoms giant Shin Corp for $1.9 billion in a tax-free deal.