Libya's political leaders signed a U.N-brokered power-sharing agreement Saturday in Morocco, but the Islamists who seized control of Tripoli last year refused to participate.
U.N. special envoy Bernardino Leon called the deal "an important step in the road to peace in Libya."
But a member of the Tripoli-based government told Reuters, "We are still in the dialogue. ... We don't really understand why they are rushing to sign before all the parties agree."
Leon and the U.S. special envoy for Libya, Jonathan Winer, both said the door remained open to any party that did not sign the deal Saturday.
Libya has been in political turmoil since longtime dictator Moammar Gadhafi was overthrown and killed in 2011.
Islamists took over Tripoli last year, setting up their own leadership and parliament and forcing the internationally recognized government to flee to the east.
Islamic State also has seized territory and has added to the chaos in Libya.