Freelance photojournalist Jeroen Oerlemans was shot in the chest and died immediately, said the spokesman, Reda Essa.
In 2012, Oerlemans was kidnapped in Syria by militants, but released after a week.
The Netherlands' ambassador to Libya, Eric Strating, saluted Oerlemans' work when tweeting condolences.
The Committee to Protect Journalists noted that Oerlemans' death
marked at least the 10th journalist, along with one media worker, killed in the Libyan conflict since it began in 2011.
"Journalists have recently begun returning in greater numbers to Libya to cover the conflict and political upheaval but it remains an extraordinarily dangerous place," said CPJ Deputy Executive Director Robert Mahoney. "The death of Jeroen Oerlemans is a reminder that those who bring us images and video from the front lines often pay the heaviest price."
Oerelmans and another photojournalist, John Cantlie, who worked for the Sunday Times of London, were held by militants in Syria from July 17-26, 2012
. A Briton, Shajul Islam, was accused in a British court of having "unlawfully and injuriously imprisoned" the two photographers.
The coastal city of Sirte is one of ISIS' last strongholds in Libya, and US-backed militias have been conducting an offensive
that has put it in danger of losing the foothold. Al-Bunyan Al-Marsous is the umbrella organization for the militias' military offensive in Sirte.
Consequently, ISIS snipers as well as IEDs have been playing even more of a role as the jihadist forces have dug in to their shrinking territory.
One doctor explained that ISIS fighters are trying to make sure their targets -- if they don't die -- will not be able to fight again.
"The snipers attack usually the spine here. They choose to fire at the spine because brain injury and heart injury if he survived, he's going to fight again," Nabeel Aqoub, a doctor working in Sirte, told CNN in September.