Winthai said reports Suthep and Prayuth had earlier communicated secretly were false.
Winthai said that prior to the coup Prayuth had been assigned by the Yingluck Shinawatra government to inform all groups involved in the conflict to find a way to hold talks.
However, efforts to do so had not been successful.
Winthai said the previous government also assigned Prayuth in his capacity as the army chief to warn all groups to avoid breaking the law. He was also instructed to protect the people.
The spokesman said Prayuth could not hold secret talks with any party as the Army had to uphold the laws.