The permanent secretary for defence told a government-backed political forum hours earlier that the Royal Thai Armed Forces were behind the poll on Feb 2 next year and added that their 400,000 personnel were ready to monitor the elections to ensure they are free and fair.
Gen Nipat echoed the military leaders' position in a meeting on Saturday.
But on stage at the Democracy Monument, Mr Suthep, who leads the People's Democratic Reform Committee, accused Gen Nipat of intentionally misinterpreting the message from the top officers.
"The permanent secretary for defence drew his own conclusion. The four did not say such a thing," he said, referring to the commanders of all forces, including Supreme Commander Gen Tanasak Patimapragorn and army leader Gen Prayuth Chan-ocha.
Mr Suthep joined the forum held by the armed forces which drew academics, officials and the private sector to discuss ways break the political impasse.
He insisted that the military leaders did not support the poll on Feb 2 as claimed by Gen Nipat.
Gen Tanasak told a press conference on Saturday that the armed forces backed the poll on condition that it be free and fair. He also offered the setting up of a panel comprising representatives of all groups and experts to supervise the election for transparency and credibility.