UN urges probe into alleged abuse of Egyptian labourers in Libya
"UNSMIL is concerned about the arrest, detention and ill-treatment of a large number of Egyptian nationals" in the city of Tarhuna, the UN mission said on Twitter.
It called on local authorities in Tripoli to "conduct a prompt investigation" into the acts which were potentially in "violation... (of) Libya's international human rights law obligations on the prohibition of torture, inhuman and degrading treatment or punishment."
A video widely circulated on social media apparently showed the Egyptian workers forced to stand on one leg with their bare feet on the sand as they raised their hands.
The men in the footage, filmed in daylight, appeared to be repeating at the behest of an unidentified man expletives against Egyptian President Abdel Fattah al-Sisi and Libya's eastern based rogue general, Khalifa Haftar.
The video drew the ire of Egyptian officials.
It "will not pass lightly and the Egyptian state does not allow assault on its citizens abroad," Egypt's immigration minister Nabila Makram was quoted as saying in local media.
On Sunday, Libya's UN-recognised Government of National Accord (GNA), based in Tripoli, said an investigation would be launched into the video's authenticity.
If proven, the interior ministry "will then present the perpetrators to the relevant judicial authorities," it said in a statement.
"Such occurrences should not spoil the strong relations between the Egyptian and Libyan people," it added.
In a Tuesday statement, the Arab League "condemned the detention and mistreatment" of the Egyptian nationals.
The bloc also welcomed the GNA "interior ministry's statement on efforts to determine the Egyptian detainees' fate and to identify the perpetrators."
Ahmed al-Mesmari, a spokesman for Haftar's forces, told a private Egyptian TV channel that the workers were being held by a "militia" aligned with the GNA.
"We have yet to determine their exact number but those who appeared in the video are between 19-22," he said, adding that it was not clear whether others were held.
Libya has been mired in chaos since the 2011 uprising that toppled and later killed longtime dictator Muammar Gaddafi.
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It is currently split between rival administrations in the east and the west.
Egypt, along with the United Arab Emirates and Russia, backs Haftar's forces, while the GNA is supported by Turkey.
Agencies contributed to this report.