The Move Forward Party (MFP) and the Pheu Thai Party, the two main coalition allies, were unable to agree on the House speaker position in their meeting with the other six parties on Sunday but said they hope to resolve the issue on Monday.
The meeting at MFP headquarters was planned to resolve the dispute over the House speaker's seat. The eight allies earlier agreed to support Move Forward leader Pita Limjaroenrat as the new prime minister.
After the meeting, Mr Pita said the eight parties had discussed the House speaker issue and the talks were positive.
However, he said, the MFP was still waiting for a definitive answer from Pheu Thai.
"If people are confused, we must apologise. We have a firm intention to form a government and solve people's problems," Mr Pita said.
He declined to comment on the possibility of another nominee for the House speaker's seat. "New speculation is not welcome because it could affect the government formation and confuse people," Mr Pita said.
Earlier the MFP said it wanted Phitsanulok MP Padipat Suntiphada to be the new House speaker while Pheu Thai stood firm it should get the seat of the head of the legislature.
Mr Pita also refused to comment when reporters asked what would happen if Move Forward and Pheu Thai were unable to eventually reach a compromise.
Pheu Thai leader Cholnan Srikaew said his party would discuss the contents of Sunday's meeting with its members on Monday and hoped his party would be able to reach a resolution on the matter.
"If the outcome is different from people's expectations, it would affect coalition allies and the formation of the government," he said. He hoped the issue would be resolved by noon on Monday.
Asked if it were possible for a political party from another bloc to nominate a different House speaker candidate instead of Pheu Thai, Dr Cholnan said: "That is difficult to answer but I am confident that every issue will be resolved by July 4."
Earlier Dr Cholnan said Move Forward should have 14 ministers' seats – plus the prime minister's – and Pheu Thai should have 14 cabinet ministers' posts plus the House speaker's seat.
Wan Muhammad Nor Matha, leader of the Prachachat Party which is one of the eight coalition allies, said he hoped the MFP and Pheu Thai would turn the next 40 hours into the time of "the people's victory" or else "the non-democratic bloc would rise".
The House secretariat set the House vote for its speaker on Tuesday.
Mr Wan Mohammad Nor said he could not reveal the content of Sunday's meeting but believed Move Foward and Pheu Thai could reach an agreement.
MFP secretary-general Chaithawat Tulathon said his party would settle the issue with Pheu Thai on Monday before the vote for the House speaker on Tuesday.