Last week Third Force fighters attacked Brak al-Shati airbase, also in southern Libya, which is controlled by Haftar forces, killing 140 people, including civilians.
"I hope first of all that asylum seekers and refugees can be taken out of detention centres," UN High Commissioner for Refugees Filippo Grandi said after visiting one centre in the Libyan capital.
LNA spokesman Ahmad al-Mesmari said the soldiers were returning from a military parade unarmed, and that most of them were executed.
Around 2,900 people were rescued Thursday, 2,300 of whom were found in international waters and taken to Italy, while 580 picked up in Libyan waters were returned to the north African country.
Members of the Third Force militia loyal to the UN-backed Government of National Accord in Tripoli attacked an airbase used by military strongman Khalifa Haftar's self-proclaimed Libyan National Army, military sources said.
Libyan authorities have complained about lacking the means to deal with the floods of refugees who try crossing the Mediterranean in makeshift boats.
The migrants, who were bound for Italy, were picked up off the western city of Sabratha, said navy spokesman Ayoub Qassem.
Remarks made in Algiers yesterday by Presidency Council foreign minister Mohamed Siala about Khalifa Hafter, seen as sympathetic to the eastern commander, have resulted in a powerful wave of criticism in Tripoli.
Six years after a revolution that toppled dictator Muammar Ghaddafi, Libya has become a key departure point for migrants risking their lives to cross the Mediterranean to Europe.
Head of Libya’s UN-backed govt meets commander of forces loyal to Tobruk-based parliament
Oil is Libya's main natural resource, with reserves estimated at 48 billion barrels, the largest in Africa.
Since Jammeh's fall, dozens of migrants who had left to go to Europe via Libya have started coming back
Kobler, on his first visit to Sudan, is expected to meet Sudanese Foreign Minister Ibrahim Ghandour and other senior officials in Khartoum.
Slated for Tuesday, election of new Libyan central bank governor is indefinitely postponed by parliamentary official
Head of Libya’s unity government calls on international community to help stop recent escalations in south
Violence escalated in southern Libya in recent days since Haftar's forces captured the Timnahent airbase
Libyan coastguards rescue 23 people but many more remain missing
An Air Force commander was among those killed in crash
Libya’s warring camps remain locked in conflict over North African country’s oil-rich central region
A US official this month told AFP that Moscow apparently has deployed military forces to a base in western Egypt.
Martin Kobler makes assertion amid continued reports of grievous rights violations across troubled nation