Authorities in control of eastern Libya on Thursday imposed foreign travel curbs on residents aged between 18 and 45, saying they would need security clearance.
"Libyan men and women aged between 18 and 45 are forbidden from leaving the country without prior security clearance from the relevant authorities," said General Abdelrazek al-Nadhouri, military commander of forces loyal to authorities in the east of Libya.
The aim was "to put in place the necessary regulations to confront dangers from abroad which threaten national security" and not to damage the rights of Libyans, he said.
The permits are to be issued by the intelligence services.
A decision announced Sunday by the same general banning women under 60 from travel abroad without a male guardian has already stirred outrage among ordinary Libyans.
Libya has been wracked by chaos since the 2011 toppling of longtime dictator Moamer Kadhafi, with rival authorities and militias battling for control of the oil-rich country.
The authorities in Libya's east have refused to recognise a UN-backed unity government in the capital Tripoli.