The UN was trying to convince Libya's warring factions on Monday to join a new round of peace talks aimed at ending months of violence and political deadlock.
The world body's mission to Libya (UNSMIL) said last week that it planned to broker new negotiations beginning on Tuesday.
But just a day before the talks were due to begin, neither the participants nor the location of talks had been announced, leading a source at UNSMIL to suggest they could be delayed.
In last week's statement, the UN mission said the main objective of the dialogue was "to reach agreement on the management of the remainder of the transitional period, until such time that a new permanent constitution is adopted".
"Discussions will focus on finding consensual solutions to the on-going institutional crisis in the country," it said, without specifying who would attend.
More than three years after dictator Moammar Gadhafi was toppled and killed in a NATO-backed revolt, the country is awash with weapons and powerful militias, and has rival governments and parliaments.
Fierce clashes persist in second city Benghazi and west of the capital Tripoli between forces loyal to the internationally recognized government and a rebel group of mainly Islamist militias.
A previous attempt to arrange U.N.-brokered talks between the warring factions in June was unsuccessful.
