Libya's internationally recognised government in Tripoli has declared a military alert after eastern forces loyal to powerful General Khalifa Haftar, said they had moved towards the western part of the country, reports Aljazeera.
"We have issued instructions and declared a general alert to all military and security forces from military and army belonging to us to be prepared," the Tripoli government said in a statement.
The eastern forces' operation, ordered by Haftar on Wednesday, is aimed at "cleansing the western zone from terrorist groups," the forces' media centre said in a statement.
"The military units confirm its keenness to protect citizens' safety and public properties of the Libyan state," the statement said without elaborating.
The deployment is likely to cause alarm in Tripoli, where Prime Minister Fayez al-Serraj has been negotiating a power-sharing deal with a parallel administration that is in the east and allied with Haftar.
In recent years, Haftar, the chief of the self-styled Libyan National Army (LNA), has expanded his foothold in large parts of Libya.
A video released by the LNA media office showed a convoy of armoured vehicles and pick-up trucks mounted with heavy guns on the road.
"In fulfilment of his [Haftar's] orders, several military units moved to the western region to purge the remaining terrorist groups located in their last hideouts," the LNA said in a statement with the video.
The statement gave no details, but the area appears to be the coastal road linking the eastern city of Benghazi, the LNA's main base, with Tripoli in western Libya.
Reporting from the Libyan capital Tripoli, Al Jazeera's Mahmoud Abdelwahed said the LNA's positioning is a display of strength.
"Many analysts and military experts in Libya say that this is some kind of show of force or power. Haftar's forces are using that to, first of all, intimidate their adversaries in the west of the country, and secondly, to test their power," he said.
"They want to see who wants to confront them in the western area."
The UN is holding a conference this month in the southwestern city of Ghadames to discuss a political solution to prepare the country for long-delayed elections and to avoid a military showdown.
Abdelwahed said it was possible that Haftar wants to reach Tripoli before the conference "so he could impose himself as a de facto security commander in the western area".
Libya has been in turmoil since the NATO-backed removal of its long-time autocrat Muammar Gaddafi in 2011.
The oil-rich country has at least two rival administrations: one based in Tripoli, and the other in the eastern city of Tobruk, which is allied with Haftar.