Ukrainian Choice leader Viktor Medvedchuk's participation in the talks with the militia on captives exchange will guarantee the fulfillment of the agreements reached, said Ukrainian Security Service spokesman Markiyan Lubkivsky.

"The Ukrainian Security Service has incorporated Medvedchuk into the process of liberating hostages and captives. This forced measures is well justified, as 150 Ukrainian citizens have already been released, including due to Medvedchuk's involvement," he said at a press briefing on Monday.

"Our citizens' lives are the most important thing for us. We are taking such a step in order to liberate our POWs. In fact, Medvedchuk guarantees that the agreements on captives exchange will be fulfilled," Lubkivsky said.

The Ukrainian Security Service's chief appointed Medvedchuk to be Ukraine's special envoy for humanitarian issues in the Contact Group for settling the conflict in eastern Ukraine, earlier reports said.

The Ukrainian Choice leader attended the Contact Group's latest round of consultations in Minsk on January 31.