UN acting Special Representative for Libya Stephanie Williams gave the estimates at a virtual meeting of the Libyan Political Dialogue Forum, Dujarric said.
The UN spokesperson explained that Williams had warned Libyan delegates that time was not on their side and that there would be a direct cost for inaction and obstruction.
"She said we are now at 20,000 foreign forces or mercenaries in the country, which she called a shocking violation of Libyan sovereignty," Dujarric said.
The forum is attempting to get Libya’s opposing military groups to establish a transitional administration to host presidential and parliamentary elections in late 2021, according to media reports.
Williams also warned of the growing humanitarian crisis that threatens to leave 1.3 million of the nation’s nearly 7 million people dependent on foreign aid by January, 2021, Dujarric said.
After the ouster and assassination of Libyan leader Muammar Gaddafi, Libya entered a period of a prolonged civil war. The country is currently divided between two centers of power — an elected parliament in the country's east, supported by the Libyan National Army and the UN-backed Libyan Government of National Accord in (GNA) the west.