Minister Ivica Dacic says Serbian authorities had been close to reaching a solution to free them
Two Serbian nationals are believed to have been killed during a US airstrike on an IS camp in Libya on Friday.
AP reports Serbian Foreign Minister Ivica Dacic named the embassy staffers as Sladjana Stankovic, a communications officer, and Jovica Stepic, a driver.
They were abducted in November after their convoy came under fire from militants near the city of Sabratha.
"We got the information, including photos, which clearly show that this is most probably true," Dacic said.
Dozens were killed in the bombing, including an operative believed to be responsible for the attacks on a Tunisian tourist report last year, according to US and local officials.
Dasic said Serbian efforts to rescue the hostages had been close to reaching a solution.
"We will seek official explanation from both Libya and the United States about the available facts and the selection of targets," he said