The sharp shooter is said to have perfected his skills during the 2011 uprising against dictator Colonel Gaddafi.
Senior ISIS terror chief Abdullah Hamad Al-Ansari has been named as the latest casualty after he was attacked on January 23 as he left a city centre mosque.
An eye witness told local news website al-Wasat: “A state of terror prevailed among the ISIS ranks after his death.Hamad Abdel Hady, an official in the depraved cult’s Sharia court, was also taken out by a sniper’s bullet earlier this month.
“They randomly shot in the air to scare inhabitants, while searching for the sniper.”
ISIS commanders are so panicked by the murders that they have carried out a number of arrests and executions in a bid to find the marksman.
It is not known if the sniper is working alone or as part of a group of anti-ISIS marksmen.
Speculation about the culprit’s identity has led to reports that the shooter hails from the neighbouring city of Misrata, which fell under ISIS control last year.
Separate rumours appeared to point the finger at American or European special forces operatives who could be taking out high-profile jihadi targets in Libya.
A crack team of British Special Forces are in Libya preparing the ground for up to 1,000 British troops who have been drafted in to tackle ISIS.
The British deployment of half a dozen elite SAS soldiers will form part of a 6,000-strong army of Americans and Europeans led by the Italian army.
The jihadi group has sought to expand its influence in the lawless north African state in a bid to seize control of Libya’s highly lucrative oil fields.
The Mediterranean port city of Sirte, just a few hundred miles from Europe’s coastline, is now the de facto base of the jihadist group’s Libyan wing.