They were killed in Libya in what appears to be a mass execution of inmates.
The video was released as Khalifa Haftar and his self-styled army declared victory in the eastern city of Benghazi.
A full video shows all 18 men drop to the floor after they are shot in the head by men in military fatigues and wearing balaclavas.
Then there is a second video that shows another two men also being shot in the head.
Later today Libya’s UN-backed Prime Minister Fayez al-Sarraj will hold talks near Paris on Tuesday with Haftar, the powerful military commander based in the country’s east.
French President Emmanuel Macron will host the meeting, the presidency said in a statement on Monday.
‘France intends, through this initiative, to facilitate a political agreement’ between the two rivals as the newly appointed UN envoy for Libya, Ghassam Salame, takes office, the statement said.
Sarraj this month laid out a new political roadmap for his violence-wracked country, including the scheduling of presidential and parliamentary elections in March 2018.
Political rivalry and fighting between militias have hampered Libya’s recovery from the chaos that followed the 2011 uprising that toppled and longtime dictator Moamer Kadhafi, who was killed in the aftermath.
Sarraj’s Government of National Accord has been struggling to assert its authority since it began work in Tripoli in March 2016. Haftar’s rival administration based in the remote east has refused to recognise it.
Western intelligence services fear that Islamic State jihadists are capitalising on the chaos to set up bases in Libya as they are chased from their former strongholds in Iraq and Syria.
Libya has also become the main springboard for migrants seeking to reach the European Union by sailing to Italy in often flimsy and overloaded boats.
French Foreign Minister Jean-Yves Le Drian told newspaper Le Monde in June that Libya was ‘a priority’ for Macron and said there was ‘a security risk because of the trafficking of all kinds, including humans’ from Libya.
‘In consultation with all its partners, France intends to show its support for the efforts to build a political compromise, under the aegis of the United Nations, which unites… all the different Libyan actors,’ Monday’s statement from the Elysee Palace said.
‘The challenge is to build a state capable of meeting the basic needs of Libyans and endowed with a regular unified army under the authority of the civil power.
‘It is necessary for the control of Libyan territory and its borders, to fight terrorist groups and arms and migrant traffickers, but also with a view to a return to a stable institutional life.’