"There are security concerns over the political process based on the direct and armed control of mercenaries in some areas, the presence of military forces with political dimensions... and the presence of some terrorists," he said.
Speaking before the start of the talks, German Foreign Minister Heiko Maas said the participants wanted to "ensure international support is there".
Standing alongside him, U.S. Secretary of State Anthony Blinken said Libya must hold its planned elections. "We share the goal of a sovereign, stable, unified and secure Libya, free from foreign interference," he added.
Helped by the United Nations, Libya has over the past year made swift progress in addressing a decade of chaos and violence that at one stage threatened to escalate into a full-scale regional conflict.
Rival administrations in the east and west of the country that had been at war with each other agreed a ceasefire and accepted the formation of Dbeibeh's unity government.
However, big risks persist with questions over all sides' commitment to the elections, and with the continued presence of myriad armed groups backed by outside powers.
Dbeibeh called on Libya's parliament to approve an election law to allow the December vote to go ahead and to pass his government's budget. "Unfortunately, we have not yet seen the necessary seriousness from the legislative bodies," he said.
Wednesday's meeting follows a previous conference in Berlin early last year that set out political, military and economic tracks to resolve a decade of chaos and violence since a NATO-backed uprising ousted Muammar Gaddafi in 2011.
The political progress emerged in the wake of eastern commander Khalifa Haftar's failed 14-month assault on Tripoli, as a new frontline solidified near the coastal city of Sirte.
Haftar was backed by the United Arab Emirates, Russia and Egypt. The Tripoli government was supported by Turkey, which ultimately helped it repel the assault.
Despite the failure of his Tripoli offensive, Haftar remains powerful and last week deployed his Libyan National Army (LNA) in the south, declaring the closure of the border with Algeria.
The two sides' October ceasefire called for the withdrawal of all foreign mercenaries by January. However, they remained in place and both sides argue over which group should leave first.
The LNA is supported by mercenaries brought by Russia's Wagner company, as well as from Sudan, Chad and Syria, a U.N. panel of experts report has said.
The former Tripoli government, which was internationally recognised, had support from Turkish regular forces in Libya as advisers, and from allied Syrian fighters.
Ankara argues that as its forces were invited by the internationally recognised government they should not be put in the same category as other foreign forces in Libya.
Two diplomats said France had prepared proposals for a sequenced withdrawal of foreign forces from Libya that was discussed with both Turkey and the United States.
However, any agreement still faced obstacles. "It is unrealistic to assume that Turkey will ever leave Libya again. They set up military bases here. Same for Russia with its Wagner mercenaries," said another diplomat.
(Reporting by Humeyra Pamuk, Joseph Nasr and Andreas Rinke in Berlin, Ahmed Elumami in Tripoli, John Irish in Paris and Tuan Gumrukcu in Ankara, Writing by Angus McDowall, Editing by William Maclean) ((Joseph.Nasr@thomsonreuters.com; +49-30-2201-33711 ;))