The United Nations chief Antonio Guterres has urged fighter groups to avoid a military escalation in Libya following the renewed conflict between rival factions in the country.
He met commander Khalifa Haftar a day after his troops launched an offensive to take capital Tripoli.
He said, he hoped it was possible to avoid a bloody confrontation in and around Tripoli.
Tunisia has tightened control on its border with Libya.
The United Nations chief met Haftar in the eastern city of Benghazi.
Forces loyal to Haftar were pushed back on Friday from a key checkpoint less than 30km from Tripoli.
Pro-government militiamen from the coastal town of Zawiya retook the base after a short exchange of fire.
The Zawiya militia is one of dozens that have proliferated since the 2011 overthrow of military ruler Muammar Qadhafi.
The United States and its allies in a joint statement urged all parties to immediately de-escalate tensions.