In a video posted on the Internet, Khalifa Haftar announced an "initiative" looking to the interim authorities being suspended.
Both the Prime Minister and the head of the armed forces poured scorn on the idea of a coup d'etat.
Haftar commanded ground forces during the 2011 uprising that overthrew the 42-year dictatorship of Moamer Gaddafi.
"The command of the Libyan national army announces its initiative for a roadmap, that will be made public in the coming days" in consultation with different parties, Haftar said in the video.
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It also looks to the formation of a presidential commission headed by the president of the Higher Judicial Council.
"The Libyan national army has decided to act... Not in order to govern but to prepare the proper conditions" for elections, Haftar said.
After Haftar's video was released, rumours quickly spread on social networks that a coup may be in the offing.
"It's a lie. The situation is under control and there is no suspect movement," the army chief of staff's spokesman Colonel Ali al-Shikhi told AFP.
"He was retired," Zeidan said, adding that state institutions were functioning normally.
It is not known if the former general has any support among the ranks of the army or from powerful groups of former rebels.
Haftar, originally from eastern Libya where the revolt against Gaddafi erupted in February 2011, served under the strongman before defecting in the late 1980s.
He returned to join the rebels after spending more than two decades in the United States.
Haftar's video comes after the GNC on February 3 took the controversial decision to extend its mandate until December, despite opposition by much of the population critical of its inability to halt Libya's slide into chaos.