The eastern-based Libyan National Army (LNA) dismissed a ceasefire announcement by authorities in the capital, Tripoli, as a marketing stunt on Sunday, saying rival forces were mobilising around front lines in the centre of the country.
Its spokesman, Ahmed Mismari, said the LNA was ready to respond to any attempted attack on its positions around the coastal city of Sirte, and Jufra, to the south.
Mismari's comments were the first by the LNA after the announcement on Friday of a ceasefire and a call for the resumption of oil production by Fayez al-Sarraj, who heads the Government of National Accord (GNA) in Tripoli, in the west.
"The initiative that Sarraj signed is for media marketing," Mismari said during a briefing for journalists. "There is a military build-up and the transfer of equipment to target our forces in Sirte."
"If Sarraj wanted a ceasefire, he would have drawn his forces back, not advanced towards our units in Sirte."
Mismari made no reference to a parallel ceasefire call also issued on Friday by the head of Libya's eastern-based parliament, Aguila Saleh.
Saleh has gained influence compared to LNA commander Khalifa Haftar since Turkish military support for the GNA forced the LNA to retreat from a 14-month offensive on Tripoli in June.
For more than five years, Libya has been divided into rival camps based in the east and west of the country.
The LNA has received backing from the United Arab Emirates, Egypt and Russia, in a conflict that has become an arena for regional rivalries.
There has been little fighting since June. In the past, both sides have accused each other of quickly violating truces and using them to rearm.