Citing humanitarian colleagues as a source, Dujarric said the casualties were victims of explosive weapons used in Qasr Bin Ghashir, Tripoli, during an airstrike on Tuesday.
He told correspondents at a regular briefing that reports of further civilian casualties from shelling on Wednesday evening were still being verified.
"Humanitarians continue to remind parties of their obligations under international humanitarian law to take all feasible measures to avoid civilian harm," the spokesman said. "They call on all parties to refrain from using explosive weapons -- including by aerial bombing or shelling -- in populated areas, given their likely indiscriminate effect."
The latest violence in Libya erupted in early April when forces allied with Gen. Khalifa Haftar advanced on the capital city, the seat of the internationally recognized Government of National Accord, just as various parties in Libya were about to sit down for talks on the beleaguered nation's future.
The renewed fighting also began during a visit by the UN secretary-general in his bid for the unification of the rival Libya factions ahead of the reunification conference.
There is no military solution to differences, Guterres said, only intra-Libyan dialogue.