The Libyan branch of the Islamic State group claimed Thursday to have executed two Tunisian journalists who went missing in September, in an online statement that sparked outrage in Tunis.
The statement on jihadist websites showing images of Sofiene Chourabi and Nadhir Ktari, saying the group had "applied the law of Allah" against them.
It was not immediately possible to independently verify the images, and the Tunisian interior ministry could not immediately confirm them.
In the jihadist statement, signed by the "communication service of the province of Barqa," the group accused the two Tunisians of having worked for "a satellite channel that fights religion".
Barqa is the Arabic name for the Cyrenaica region of eastern Libya where IS is thought to have gained a foothold.
One picture showed the two young men at the time of their arrest alongside an armed man in fatigues, his face covered.
The fourth and final photo is almost totally black. It appears to show a bullet being fired at a kneeling person and carries the Muslim profession of faith -- "there is no God but God and Mohammed is His messenger."
A caption speaks of "implementing the rule of Allah on Chourabi and Ktari, those who fought Allah and sowed corruption in the land."
Chourabi, an investigative journalist and blogger who was active during Tunisia's 2011 revolution, and Ktari, a photographer, went missing in the Ajdabiya district of eastern Libya on September 8.
The two had been taken captive by an armed group near the town of Brega, further west, on September 3, but were released a few days later after the Tunisian authorities intervened.
Media watchdog Reporters Without Borders (RSF), which said they were working for a new Tunisian channel called First TV, said they were subsequently arrested by a militia and then disappeared.
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RSF expressed its "serious concern" over their situation and called on "everyone involved in Libya's transition to work toward their return safe and sound to Tunisia."
- Tearful vigil -
Thursday's news sparked horror in Tunisia, particularly on social media networks, where people expressed their shock and disbelief, many expressing hope because there had not been any official confirmation.
Dozens of people, mostly journalists and many in tears, gathered outside the headquarters of the journalists' union in Tunis to wait for news, an AFP photographer reported.
An interior ministry official said "we are still not certain of the veracity of these photos," adding that the men had been arrested by "radical Islamists" at a roadblock near the city of Derna, many kilometres (miles) to the northeast of Ajdabiya.
For his part, Foreign Minister Mongi Hamdi told Express FM radio "we hope this information is not true. These are innocent journalists who went to Libya to do their job."
Hamdi expressed frustration over failed efforts to secure the two men's release, saying "we do not know who kidnapped them, why they kidnapped them or where they are."
Libya has been engulfed by chaos since the 2011 NATO-backed uprising that toppled and killed veteran dictator Moamer Kadhafi, with two rival governments and a host of militias now vying for territory.
IS has seized swathes of Iraq and Syria, declaring a "caliphate" and committing widespread atrocities, including the beheading of Western hostages.