The militants in Donbas are holding 684 Ukrainian captives, most of whom should hopefully be freed by the end of the year, Ukrainian Security Service main investigative department chief Vasyl Vovk said at a press conference in Kyiv on Wednesday.

"We think we will have most of these people freed as early as [by the end of] this year. We are working on confirming the lists and having our people freed now," Vovk said.

When asked to specify how many people are being held captive, Vovk said the Security Service has accounted for 684 people.

"They are ready to hand over 152 people to us," Vovk said.