Representatives from the Election Commission (EC), the Office of the Ombudsman, the National Anti-Corruption Commission (NACC), the State Audit Commission, the National Human Rights Commission (NHRC) and the National Economic and Social Advisory Council (Nesac) on Monday said they would ask the government and the People's Democratic Reform Committee (PDRC) to each nominate 10 neutral people to mediate future peace talks.
But PDRC secretary-general Suthep immediately said the idea is doomed to fail because neither party will be able to agree on suitable go-betweens.
Ms Yingluck has now also rejected the plan as futile.
"It is right to ask neutral people to mediate peace talks, but they must be equal and guidelines must be applicable," Ms Yingluck said. "I have to do my job in line with the law and preserve the democratic system, not protect the government's power."
The premier said she had never hindered the military's role as a potential mediator between the government and the PDRC.
She added that she had not insisted the PDRC end their protests or the general election be concluded before negotiations can be held.
Her only request is that negotiations must be held within the constitutional framework, she said.
Ms Yingluck called on all sides to follow the advice of His Majesty the King given on Dec 5 last year, when he urged all Thai citizens to perform their individual duties with integrity and to the utmost of their abilities.