Kidnappers have seized Egypt's cultural attache and three other embassy staff in the Libyan capital Tripoli, a day after a group snatched another Egyptian official in the city.
The kidnappings of Friday and Saturday forced Egypt to evacuate its Tripoli embassy and its Benghazi consulate.
Egypt's state news agency MENA said the Egyptian ambassador and numerous diplomats and their families had arrived back in Cairo.
Calling themselves Libyan revolutionaries, the self-proclaimed kidnappers contacted Dubai-based Al Arabiya television channel to demand the release in 24 hours of Shaban Hadia, a Libyan armed group chief, and put one of the Egyptian diplomats on the line.
"The kidnappers have demands and we ask these demands are met and the defendant Abu Hadia be released," a man called Shirbini from the Egyptian cultural centre told the channel.
Hadia is a commander in the Operations Room for Libya Revolutionaries, one of the many armed groups which fought Muammar Gaddafi, Libya's long-time ruler, during the 2011 NATO-backed uprising, but have since refused to disarm and accept Tripoli's authority.
"We won't free the diplomats unless the sheikh is freed within 24 hours," one of the supposed kidnappers said, without giving details of what would happen after that deadline.
Libyan officials said they were in contact with the kidnappers while an Egyptian Foreign Ministry spokesman confirmed that Hadia was under investigation in Egypt.
"If there is no charge at the end of it, then he will be released," the spokesman told Al Arabiya.
"He will be treated kindly and we expect good treatment of the Egyptians."
The abductions of the diplomats came as fighting in the south and west of Libya claimed more than 150 lives, adding to the sense of chaos in the North African country, more than two years after rebels overthrew and killed Gaddafi.
The Operations Room for Libya Revolutionaries has formally denied it is involved in the kidnappings, but on Friday it had given warning that there would be a strong response if Hadia was not released.
"What we have been warning the Egyptian authorities about since yesterday is that this kind of response was to be expected because of the security situation in the country," Adel al-Gharyani, a commander, told Reuters news agency.
The Operations Room, whose former rebel fighters were nominally hired by the government to secure Tripoli, was accused of briefly abducting Ali Zeidan, Libyan prime minister, in Tripoli in October last year.
The group first claimed it had arrested Zeidan, only to deny it was involved when he was released after several hours.
Zeidan, a liberal, had upset Libyan Islamists last year when he visited Egyptian chief of staff General Abdel Fattah el-Sisi after the military deposed Egypt's Islamist president, Mohamed Morsi, following protests against his rule.
Loyal to factions
Libya's General National Congress is split between the Islamist JCP party, political wing of the Muslim Brotherhood, and the nationalist National Forces Alliance.
Some armed brigades are allied to rival political factions.
Thousands of former fighters are on the government payroll associated with the Interior Ministry or the Defence Ministry in an attempt to coax them to join regular armed forces.
But many still stay loyal to their brigade commanders.
One former rebel commander who worked for the state-run Petroleum Facilities Guards defected in August.
He has since seized three key oil ports and held them for months to demand more autonomy from the central government in Tripoli.