The UN on Thursday warned against "provocation" in Libya that could lead to clashes, citing reports of armed elements mobilising around the capital Tripoli, as rival governments vie for power.
Tensions have simmered since the country's eastern-based parliament swore in a prime minister earlier this month in a challenge to interim premier Abdulhamid Dbeibah.
Dbeibah has refused to hand over power to Fathi Bashagha, an ex-interior minister named by parliament as premier, and says he is the country's rightful steward until elections are held.
The UN mission in Libya (UNSMIL) expressed concern on Twitter over "reports about the mobilisation of forces and movement of large convoys of armed groups that have increased tensions in and around Tripoli".
Stephanie Williams, UN chief Antonio Guterres' special adviser on Libya, has been attempting to mediate between the two sides.
"I urge restraint and the need to abstain from provocative actions, in word and deed, including the mobilisation of forces," she tweeted on Thursday.
"I renew my offer to utilise the good offices of the United Nations to mediate and assist Libyans in finding a consensual way forward."
Video footage and pictures posted online Thursday purportedly showed convoys of militiamen loyal to Bashagha massing east of the Libyan capital, feeding expectations that they were poised to enter Tripoli.
Bashagha has yet to arrive in the capital, but has insisted he will govern the country "by force of the law" from Tripoli.
An AFP correspondent witnessed dozens of pick-up trucks mounted with machine guns and other military hardware east of Tripoli, along a coastal road.
Construction tycoon Dbeibah was appointed early last year following a landmark 2020 ceasefire with a mandate to lead the country to elections that were due to take place in December 2021.
His appointment initially generated cautious hopes that the country could move beyond a decade of conflict following the NATO-backed 2011 revolt that toppled and killed dictator Muammar Gaddafi.
But bitter disputes over the constitutional and legal basis of those elections and the presence of controversial candidates led to the vote being indefinitely postponed.
On Thursday, the US ambassador in Libya, Richard Norland, also expressed fears over an escalation.
"We fully support UNSMIL's message and urge both sides to seize the opportunity to pursue a political solution rather than risk escalation," he said on Twitter.