Thai opposition leader Suthep Thaugsuban has given Prime Minister Yingluck Shinawatra two days to resign as anti-government protests spiral further out of control.
Suthep, who is spearheading the protests, gave the ultimatum during a secret meeting mediated by the army.
After Yingluck fled to an undisclosed location as protesters launched a "People's Coup", military chief Prayuth Chan-ocha coordinated talks between the leaders, the first since the week-long protests began.
Top military commanders, including naval and air force chiefs, were also present during the hour-long meeting.
However, the talks failed to yield any concrete result as Suthep refused to accept any outcome bar Yingluck's resignation.
"I did not regard the meeting as a negotiation. I told her to return the ruling mandate to people. A council should be set up to draft a new constitution before holding a new election," the opposition leader said at a press conference following the meeting.
He added: "This would be the only meeting between the premier and me, and there will be no meetings until the people win. I decided to attend the meeting because it was held in the presence of the armed forces' commanders-in-chief. It was a good opportunity to make them aware of the people's stance in a clear and straightforward manner."
Suthep said Yingluck did not respond to any of his demands during the talks. However, the army chief has made it clear that the spiralling violence during the rallies must be halted.
Neither the military nor Yingluck's office has officially released an account of the secret meeting as yet.
Meanwhile the government has urged the residents of Bangkok and other places to remain indoors, warning them that violence could break out during the anti-government rallies.
Thailand's Deputy Prime Minister Pracha Promnok insisted that the government is in control of the situation despite the ongoing protests, which have killed at least four people.
The anti-government protests began against a controversial amnesty bill, which, the opposition claims, intends to bring back former prime minister and Yingluck's brother Thaksin Shinawatra from his self-imposed exile.
Thaksin himself was ousted from power in 2006 during a military coup.