"Four more have been kidnapped. One of them is the cultural attaché and the other three are staff," the Libyan Foreign Ministry spokesman said, without elaborating.
An Egyptian foreign ministry spokesman, Badr Abd-al-Ati, said that the abducted attache had contacted embassy staff in Tripoli to say he was being well-treated.
Another embassy official was seized in the Libyan capital on Friday.
No group claimed responsibility for the abductions, but incident came soon after a powerful Libyan militia reported its leader had been arrested in Cairo and threatened to retaliate.
Two years after Libyan dictator Muammar Gaddafi's fall, the country is still in flux with the government struggling to control heavily-armed former rebels and militants who fought in the uprising but often challenge Tripoli's authority.
One militia group, the Operations Room of Libya's Revolutionaries, said on Friday its leader Shaban Hadia had been arrested in Egypt, where he had been travelling with his family for medical treatment.
Another of the group's leaders, Adel al-Gharyani, denied it had kidnapped the first Egyptian diplomat. But he called on Egyptian authorities to release their commander or there would be a "strong response" from the group.
A number of foreigners have been kidnapped and attacked in recent weeks. Libyan security forces earlier this week freed a South Korean trade official who had been held for days by kidnappers who authorities said were not politically motivated.
RA/MB