Britain, France, Germany, Italy, Spain and the United States urged the parties to sign a proposed deal at talks in Morocco and called for peace in the violence-wracked country.
"We urge all Libyan parties to sign in the coming days the political agreement presented by the UN," said a joint statement from the nations.
Libya's rival parliaments have been locked in talks in Morocco, and on Monday UN envoy Bernardino Leon said he hoped they would endorse his proposals for a unity government this week after they failed to do so at the weekend.
The six countries said they welcomed the proposal and supported the formation of a Government of National Accord.
"We consider this document a thoughtful, well-balanced basis for agreement that meets the urgent expectations of Libyan people and secures the unity of Libya," they said.
Plunged into chaos since the overthrow of Muammar Qaddafi's regime in 2011, Libya has two parliaments - and two governments - vying for power, one in Tripoli and one in the eastern port city of Tobruk, which is recognized by the international community.
Rising violence and the growth of extremist organizations, including the Islamic State group, on Europe's doorstep has prompted international pressure to resolve the crisis.
In the statement, the countries expressed "deep concern about the ongoing violence within Libya, and the expansion of terrorism in Libya."
"We reiterate that there is no military solution to this crisis and we underline that the economic and humanitarian situation is worsening every day."
The countries also said various peace bids, including "local-level ceasefires, prisoner exchanges, and the return of internally displaced persons" were important routes to restoring stability and did not rule out the possibility of imposing economic penalties.
"The international community stands ready to hold accountable through sanctions those who threaten Libya's peace, stability and security," the statement read.
The latest talks between the rival parliaments, the first face-to-face discussions since March, are set to resume on Thursday after both sides hold separate consultations.