The UN envoy to Syria, Geir Pedersen, warned of ISIS mercenaries strengthening their activities in central and northern Syria, and demanded Damascus to release the detainees.

Today, Wednesday, Geir Pedersen said, "The United Nations is not involved in the upcoming Syrian presidential elections."

In his remarks, Pederson urged the Damascus government to "release the detainees."

The UN envoy stressed the need to make progress in the files of "detainees and missing persons in Syria."

Pederson warned of "the ISIS activity strengthening in central and northern Syria."