Thousands rally in support of Libya's military strongman Haftar
In a televised speech, Haftar - who has never recognised the GNA's authority - said the "expiry of the Libyan political accord" marked a "historic and dangerous turning point".
"All bodies resulting from this agreement automatically lose their legitimacy, which has been contested from the first day they took office," he said.
The head of the eastern-based internationally recognised parliament Agila Saleh later on Sunday called for parliamentary and presidential elections to be held in 2018, likely in response to Haftar's remarks.
"I call upon the Libyan people to participate in the upcoming parliamentary and presidential elections," he said in a TV broadcast.
"It is the only way to peacefully and democratically transfer power."
The UN said on Sunday that it was "intensively trying to establish the proper political, legislative and security conditions for elections to be held before the end of 2018".
Libya has been wracked by lawlessness ever since the NATO-backed overthrow of long-time dictator Muammar Gaddafi in 2011.
Through military success, Haftar has marked himself as a key player in Libya, having also received backing from Egypt, the UAE and tacit support from Russia.
Rights groups, however, have accused his forces, the Libyan National Army (LNA), of committing dozens of extrajudicial executions which could amount to war crimes.