The move underlined the devastating impact of what is described by the United Nations as foreign interference, which the UN's special envoy Ghassan Salame said had to stop.
The meeting in the German capital, Berlin, will bring the two sides together, along with their foreign backers, the United Nations and other global powers, including Russia's President Putin and Turkish President Recep Tayyip Erdogan.
Global players must stop meddling in the Libyan conflict, the UN's special envoy told AFP on Saturday, on the eve of a summit of world powers to try to bring peace to the North African nation.
After months of combat, which has killed more than 2,000 people, a ceasefire came into effect Sunday backed by both Ankara and Moscow, which is accused of supporting Haftar.More news: Seven missing after avalanche hits Nepalese trekking route
Heads of state and lawmakers from Russia, Algeria, Turkey, Egypt, the United Arab Emirates, France, Italy, Britain, China and the USA gathered in Berlin before a key summit to discuss the future of Libya kicks off on Sunday.
"The conference can be the first step to peace for Libya", Maas told the Bild newspaper.
Sarraj meanwhile issued a call for worldwide "protection troops" if Haftar were to keep up his offensive. Greece also seems to have backed off from its veto threat, alluding that an expression by the European Union of its disapproval of the deal could be enough.
He called on European nations to "show the world that it is a relevant actor in the global arena" saying "terrorist organizations such as ISIS and Al-Qaeda, which suffered a military defeat in Syria and Iraq, will find a fertile ground to get back on their feet".
Erdogan also played up Europe's fears of a repeat of the 2015 refugee crisis. In a commentary for Politico news website, he warned that further unrest could prompt a new wave of migrants to head for the continent.More news: Ireland surprises West Indies at T20I opening
"To leave Libya at the mercy of a warlord would be a mistake of historic proportions", Erdogan said, referring to Haftar.
Tarek Megerisi, a policy fellow with the North Africa and Middle East programme at the European Council on Foreign Relations, said there was no sign Haftar's backers were pushing him to stop the war.
For Turkey, the GNA's fall would risk jeopardising a maritime boundary agreement the parties signed.
Serraj's government is backed by Turkey, Qatar and Italy while Hifter is supported by Egypt, the United Arab Emirates, Saudi Arabia and France.
Erdoğan arrived in Berlin on January 19 to attend an worldwide conference on Libyan peace.More news: Bruno in the dark about Man United Transfer, says Silas
"Yet the risk remains that some participants will merely pay lip service to the diplomatic initiative, even as they continue to fuel a war from which they benefit".